ArmVirtPkg: Perform Arm CCA initialisation in the Pei phase

Add ArmCcaInitialize () to perform Arm CCA specific initialisation
like:
 - Reading the Realm Config by calling the RSI interface.
 - Storing the IPA width of the Realm in PcdArmCcaEarlyIpaWidth.
 - Configuring the MMIO regions to update the page tables to set
   the protection attribute as Unprotected IPA.

Note: ArmCcaInitialize () is implemented in ArmCcaInitPeiLib for
which a Null implementation is provided. Therefore, this change
should not break existing platforms that do not implement the
Arm CCA.

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