ArmVirtPkg: RMM 1.0-eac2 - Update RsiRealmConfig structure

The RMM 1.0-eac2 specification updates the RsiRealmConfig
structure to add a new member to identify the Realm hash
algorithm.

Therefore, update the REALM_CONFIG structure to add a
new member HashAlgorithm that represents the Realm hash
value. Also add macros to define the RsiHashAlgorithm
enumeration values SHA-256 and SHA-512.

Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>