Enable MPU regions for AM654 evm:
- Region0: 0x00000000 - 0xFFFFFFFF: Device memory, not executable
- Region1: 0x41c00000 - 0x42400000: Normal, executable, WB, Write alloc
- Region2: 0x80000000 - 0xFFFFFFFF: Normal, executable, WB, Write alloc
- region3-15: Disabled

With this dcache can be enabled either in SPL or U-Boot.
Reviewed-by: NTom Rini <trini@konsulko.com>
Signed-off-by: NLokesh Vutla <lokeshvutla@ti.com>