ArmVirtPkg: Define an interface to configure MMIO regions for Arm CCA

The IPA space of a Realm is divided into two halves:
  - Protected IPA space and
  - Unprotected IPA space.

Software in a Realm should treat the most significant bit of an
IPA as a protection attribute.

The Unprotected IPA space is used for sharing memory and for performing
MMIO accesses with the Host.

An Unprotected IPA is an address in the upper half of a Realm's
IPA space. The most significant bit of an Unprotected IPA is 1.

Therefore, the page tables for the MMIO regions must be updated to set
the most significant bit of the IPA space.

To facilitate this define ArmCcaConfigureMmio () that can be called
during the early firmware startup.

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