ArmVirtXen.dsc initializes
gEfiMdeModulePkgTokenSpaceGuid.PcdFirmwareVersionString with with the
value of the variable "FIRMWARE_VER".
Move that functionality to ArmVirt.dsc.inc to make it available to all
ArmVirt packages, and make it conditional: only set the PCD string if
FIRMWARE_VER is actually defined.
This allows specifying the firmware version string on the build command
line with -D FIRMARE_VER=...
Signed-off-by: Oliver Steffen <osteffen@redhat.com>
Reviewed-by: Sami Mujawar <sami.mujawar@arm.com>