ArmVirtPkg: ArmCcaRsiLib: Add interfaces to get/extend REMs

The Section A2.1.3 Realm attributes, RMM Specification, version A-bet0
introduces the concept of REMs as described below:
  DGRFCS - A Realm Extensible Measurement (REM) is a measurement value
           which can be extended during the lifetime of a Realm.
  IFMPYL - Attributes of a Realm include an array of measurement values.
           The first entry in this array is a RIM. The remaining entries
           in this array are REMs.

The Realm Service Interface commands defined in section
B4.3.7 RSI_MEASUREMENT_READ and B4.3.6 RSI_MEASUREMENT_EXTEND
specify the interfaces to read and extend measurements to REMs.

Therefore, update ArmCcaRsiLib to add interfaces to get and extend REMs.

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