fix(U-Boot): update defconfig names for AM62x SiP

The name 'AM6254atl' was chosen for the AM62x SiP as part of upstreaming
the board support[1].

This patch updates the U-Boot build steps to reflect the updated
defconfig names for the platform.

[1]: https://lore.kernel.org/all/20251025-62sip_support-v3-0-b4c8314d0055@ti.com/

Signed-off-by: Anshul Dalal <anshuld@ti.com>

Author: ArchUsr64

source/linux/Foundational_Components/U-Boot/BG-Build-K3.rst

@@ -283,8 +283,8 @@ All of these binaries are available in the SDK at :file:`<path to tisdk>/board-s
    |  AM62X LP SK  | ``am62x_lpsk_r5_defconfig``        | ``am62x_lpsk_r5_defconfig am62x_r5_usbdfu.config``       | ``am62x_lpsk_r5_defconfig am62x_r5_usbmsc.config``       |
    |               | ``am62x_lpsk_a53_defconfig``       | ``am62x_lpsk_a53_defconfig``                             | ``am62x_lpsk_a53_defconfig``                             |
    +---------------+------------------------------------+----------------------------------------------------------+----------------------------------------------------------+
-   |  AM62SIP SK   | ``am62xsip_evm_r5_defconfig``      | ``am62xsip_evm_r5_defconfig am62x_r5_usbdfu.config``     | ``am62xsip_evm_r5_defconfig am62x_r5_usbmsc.config``     |
-   |               | ``am62xsip_evm_a53_defconfig``     | ``am62xsip_evm_a53_defconfig``                           | ``am62xsip_evm_a53_defconfig``                           |
+   |  AM62SIP SK   | ``am6254atl_evm_r5_defconfig``     | ``am6254atl_evm_r5_defconfig am62x_r5_usbdfu.config``    | ``am6254atl_evm_r5_defconfig am62x_r5_usbmsc.config``    |
+   |               | ``am6254atl_evm_a53_defconfig``    | ``am6254atl_evm_a53_defconfig``                          | ``am6254atl_evm_a53_defconfig``                          |
    +---------------+------------------------------------+----------------------------------------------------------+----------------------------------------------------------+
 
    .. note::
@@ -320,21 +320,24 @@ All of these binaries are available in the SDK at :file:`<path to tisdk>/board-s
       $ make ARCH=arm CROSS_COMPILE="$CROSS_COMPILE_32" O=$UBOOT_DIR/out/r5 BINMAN_INDIRS=$TI_LINUX_FW_DIR
 
       For AM62SIP
-      NOTE: AM62SIP Uses config fragment model.
-      $ make ARCH=arm CROSS_COMPILE="$CROSS_COMPILE_32" am62x_evm_r5_defconfig am62xsip_sk_r5.config O=$UBOOT_DIR/out/r5
+      $ make ARCH=arm CROSS_COMPILE="$CROSS_COMPILE_32" am6254atl_evm_r5_defconfig O=$UBOOT_DIR/out/r5
       $ make ARCH=arm CROSS_COMPILE="$CROSS_COMPILE_32" O=$UBOOT_DIR/out/r5 BINMAN_INDIRS=$TI_LINUX_FW_DIR
 
       A53
       To build tispl.bin and u-boot.img. Saved in $UBOOT_DIR/out/a53. Requires bl31.bin, tee-pager_v2.bin
 
-      For AM62X or AM62SIP
+      For AM62X
       $ make ARCH=arm CROSS_COMPILE="$CROSS_COMPILE_64" am62x_evm_a53_defconfig O=$UBOOT_DIR/out/a53
       $ make ARCH=arm CROSS_COMPILE="$CROSS_COMPILE_64" CC="$CC_64" BL31=$TFA_DIR/build/k3/lite/release/bl31.bin TEE=$OPTEE_DIR/out/arm-plat-k3/core/tee-pager_v2.bin O=$UBOOT_DIR/out/a53 BINMAN_INDIRS=$TI_LINUX_FW_DIR
 
       For AM62X LP
       $ make ARCH=arm CROSS_COMPILE="$CROSS_COMPILE_64" am62x_lpsk_a53_defconfig O=$UBOOT_DIR/out/a53
       $ make ARCH=arm CROSS_COMPILE="$CROSS_COMPILE_64" CC="$CC_64" BL31=$TFA_DIR/build/k3/lite/release/bl31.bin TEE=$OPTEE_DIR/out/arm-plat-k3/core/tee-pager_v2.bin O=$UBOOT_DIR/out/a53 BINMAN_INDIRS=$TI_LINUX_FW_DIR
 
+      For AM62SIP
+      $ make ARCH=arm CROSS_COMPILE="$CROSS_COMPILE_64" am6254atl_evm_a53_defconfig O=$UBOOT_DIR/out/a53
+      $ make ARCH=arm CROSS_COMPILE="$CROSS_COMPILE_64" CC="$CC_64" BL31=$TFA_DIR/build/k3/lite/release/bl31.bin TEE=$OPTEE_DIR/out/arm-plat-k3/core/tee-pager_v2.bin O=$UBOOT_DIR/out/a53 BINMAN_INDIRS=$TI_LINUX_FW_DIR
+
 
 .. ifconfig:: CONFIG_part_variant in ('AM62AX')