ArmVirtPkg: Add ArmCcaDxe for early DXE phase initialisation

Add ArmCcaDxe for early DXE phase initialisation like setting
up the monitor call conduit for Realm code

The Realm code should use SMC as the conduit for monitor calls.
Therefore, set the PcdMonitorConduitHvc to FALSE if the code is
running in a Realm.

Note: ArmCcaDxe is configured as an APRIORI DXE so that the DXE
dispatcher can schedule this to be loaded at the very beginning
of the Dxe phase. The DevicePathDxe.inf and Pcd.inf modules have
also been included to satisfy the required dependencies.

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