ArmVirtPkg: IoMMU driver to DMA from Realms

On Arm CCA systems the access to pages inside the Realm is protected.

However, software executing in a Realm needs to interact with the
external world. This may be done using para virtualisation of the
disk, network interfaces, etc. For this to work the buffers in the
Realm need to be shared with the Host. The sharing and management
of the Realm buffers is done by the Realm Aperture Management
Protocol, which invokes the necessary Realm Service Interfaces
to transition the buffers from Protected IPA to Unprotected IPA.

The ArmCcaIoMmu driver provides the necessary hooks so that DMA
operations can be performed by bouncing buffers using pages shared
with the Host. It uses the Realm Aperture Management protocol to
share the buffers with the Host.

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