board: armltd: Add support for Total Compute platform

Total Compute is based on ARM architecture and has
the following features enabled in u-boot:
- PL011 UART
- PL180 MMC
- NOR Flash
- FIT image with Signature
- AVB

Signed-off-by: Usama Arif <usama.arif@arm.com>
Reviewed-by: Tom Rini <trini@konsulko.com>