configs: j721e_sk: Move to separate defconfig for J721E SK board

Add defconfig for J721E SK R5 and A72 configuration.

This includes and modifies the J721E EVM defconfigs:
j721e_evm_r5_defconfig -> j721e_sk_r5_defconfig
j721e_evm_a72_defconfig -> j721e_sk_a72_defconfig

Signed-off-by: Neha Malcom Francis <n-francis@ti.com>
7 files changed