ArmVirtPkg: Add Arm CCA Realm Service Interface Library

The Realm Management Monitor (RMM) is a software component which
forms part of a system which implements the Arm Confidential Compute
Architecture (CCA) and is responsible for management of Realms.
The RMM specification defines a Realm Service Interface (RSI) that
the Guest can use to request services from the RMM.

Therefore, add a library that implements the RSI interfaces to:
  - query the RSI version
  - get the Realm configuration.

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