configs: am68_sk: Move to separate defconfig for AM68 SK board

Add defconfig for AM68 SK R5 and A72 configuration.

This includes and modifies the AM68 EVM defconfigs:
j721s2_evm_r5_defconfig -> am68_sk_r5_defconfig
j721s2_evm_a72_defconfig -> am68_sk_a72_defconfig

Reviewed-by: Neha Malcom Francis <n-francis@ti.com>
Signed-off-by: Manorit Chawdhry <m-chawdhry@ti.com>
7 files changed