Enable Verified Boot

Verified boot can only be enabled or disabled at build time.

In BoardConfig.py, change the following entries:

# OS_PK | FWU_PK | CFG_PK | FWU_PLD | PLD | Stage2 | Stage1B
# Stage1B is verified by CSE
self.VERIFIED_BOOT_HASH_MASK  = 0x00000056

When the bit for a component is 1 in VERIFIED_BOOT_HASH_MASK, SBL verifies the digest for the corresponding component.

One can replace a new key in BootloaderCorePkg/Tools/Keys.