feat(linux): U-Boot: Build: document falcon support for AM62l

Falcon mode support for AM62l can be enabled using the
am62lx_falcon.config U-Boot config fragment with no changes to the rest
of rootfs.

This patch documents the same in U-Boot's build process.

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

Author: ArchUsr64

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

@@ -458,6 +458,15 @@ All of these binaries are available in the SDK at :file:`<path to tisdk>/board-s
          BINMAN_INDIRS=$TI_LINUX_FW_DIR \
          TEE=$OPTEE_DIR/out/arm-plat-k3/core/tee-pager_v2.bin
 
+   .. note::
+
+      The :file:`am62lx_falcon.config` config fragment can be used to enable
+      falcon mode support.
+
+      .. code-block:: console
+
+         $ make CROSS_COMPILE="$CROSS_COMPILE_64" am62lx_evm_defconfig am62lx_falcon.config
+
 .. ifconfig:: CONFIG_part_variant not in ('AM64X', 'AM62X', 'AM62AX', 'AM62LX')
 
    .. note::