ArmVirtPkg: ArmCcaRsiLib: Add an interface to make a RSI Host Call

The Section A4.5 Host call, RMM Specification, version A-bet0
describes the programming model for Realm communication with
the Host and specifies the following:
  DYDJWT - A Host call is a call made by the Realm to the Host, by
           execution of the RSI_HOST_CALL command.
  IXNFKZ - A Host call can be used by a Realm to make a hypercall.
  DYDJWT - A Host call is a call made by the Realm to the Host, by
           execution of the RSI_HOST_CALL command.

Therefore, introduce definition of HOST_CALL_ARGS structure that
represents the arguments to the RSI_HOST_CALL command as defined
in Section B4.3.3 RSI_HOST_CALL command.

Also update the ArmCcaRsiLib library to add a new interface
RsiHostCall () to make a Host call.

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