ArmVirtPkg: RMM 1.0-eac4 - Add RSI Features support

The RMM 1.0-eac4 introduces a new FID  RSI_FEATURES
to query the RSI features supported that have been
implemented.

Therefore, introduce a new function RsiGetFeatures
to query the features supported by the RSI.

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