docs(u-boot): Update documentation with device specific config snippet

Update Ethernet boot documentation with device specific config snippet to
avoid adding the same code-block for every device. Also add config
variables of the device for which documentation already exist, AM64X and
AM62X.

Signed-off-by: Chintan Vankar <c-vankar@ti.com>

Author: chintanv133

configs/AM62X/AM62X_linux_config.txt

@@ -31,6 +31,10 @@ Replacement Variables
 '__FEATURINGMATRIX__'            : \
 '__SYSFW_CORE_NAME__'            : 'TIFS'
 '__IMAGE_TYPE__'                 : 'default'
+'__SPL_VCI_STRING_LEN__'         : '19'
+'__SPL_VCI_STRING__'             : 'AM62X U-Boot R5 SPL'
+'__UBOOT_VCI_STRING_LEN__'       : '20'
+'__UBOOT_VCI_STRING__'           : 'AM62X U-Boot A53 SPL'
 
 Configuration Values
 --------------------

configs/AM64X/AM64X_linux_config.txt

@@ -33,6 +33,10 @@ Replacement Variables
 '__PCIE_BASE_ADDRESS__'          : 'f102000'
 '__PCIE_DEVICE_ID__'             : '0xb010'
 '__IMAGE_TYPE__'                 : 'default'
+'__SPL_VCI_STRING_LEN__'         : '19'
+'__SPL_VCI_STRING__'             : 'AM64X U-Boot R5 SPL'
+'__UBOOT_VCI_STRING_LEN__'       : '20'
+'__UBOOT_VCI_STRING__'           : 'AM64X U-Boot A53 SPL'
 
 Configuration Values
 --------------------

source/linux/Foundational_Components/U-Boot/UG-Network-K3.rst

@@ -50,48 +50,22 @@ binaries files to be sent over TFTP are listed in the table below.
         - Disable link info Bootmode pin so that ROM can identify the PHY and establishes link with the supported speed and duplex mode.
         - Please note that due to MDIO corruption (Errata i2329), booting over Ethernet is not recommended for production purposes.
 
-.. ifconfig:: CONFIG_part_variant in ('AM64X')
-
-  If using ISC dhcpd an example host entry would look like this:
-
-  .. code-block:: text
-
-      subnet 10.0.0.0 netmask 255.0.0.0
-      {
-        range dynamic-bootp 10.0.0.2 10.0.0.16;
-        if substring (option vendor-class-identifier, 0, 16) = "TI K3 Bootp Boot"
-        {
-          filename "tiboot3.bin";
-        } elsif substring (option vendor-class-identifier, 0, 20) = "AM64X U-Boot R5 SPL"
-        {
-          filename "tispl.bin";
-        } elsif substring (option vendor-class-identifier, 0, 21) = "AM64X U-Boot A53 SPL"
-        {
-          filename "u-boot.img";
-        }
-
-        range 10.0.0.17 10.0.0.25;
-        default-lease-time 60000;
-        max-lease-time 720000;
-        next-server 10.0.0.1;
-      }
-
-.. ifconfig:: CONFIG_part_variant in ('AM62X')
+.. ifconfig:: CONFIG_part_variant in ('AM64X','AM62X')
 
   If using ISC dhcpd an example host entry would look like this:
 
-  .. code-block:: text
+  .. parsed-literal::
 
       subnet 10.0.0.0 netmask 255.0.0.0
       {
         range dynamic-bootp 10.0.0.2 10.0.0.16;
         if substring (option vendor-class-identifier, 0, 16) = "TI K3 Bootp Boot"
         {
           filename "tiboot3.bin";
-        } elsif substring (option vendor-class-identifier, 0, 20) = "AM62X U-Boot R5 SPL"
+        } elsif substring (option vendor-class-identifier, 0, |__SPL_VCI_STRING_LEN__|) = "|__SPL_VCI_STRING__|"
         {
           filename "tispl.bin";
-        } elsif substring (option vendor-class-identifier, 0, 21) = "AM62X U-Boot A53 SPL"
+        } elsif substring (option vendor-class-identifier, 0, |__UBOOT_VCI_STRING_LEN__|) = "|__UBOOT_VCI_STRING__|"
         {
           filename "u-boot.img";
         }