ArmVirtPkg: Define a GUID HOB for IPA width of a Realm

The IPA width of a Realm is read from the Realm Config by invoking
the RSI call RSI_REALM_CONFIG to read the Realm Config. The IPA width
is then stored in a GUID HOB gArmCcaIpaWidthGuid for subsequent use.

This GUID HOB is also useful to pass the IPA width of the Realm to the
DXE phase.

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