Basetools/GenFw: Allow AARCH64 builds to use the --prm flag

Basetools/GenFw: Allow AARCH64 builds to use the --prm flag

The GenFw invocation with the --prm flag was previously reserved for
X64.
AArch64 platforms, built with GCC5, can also deploy PRM modules, hence
the --prm flag is also applicable in builds targeting the AARCH64
architecture.

This commit enables the --prm flag to be used for EDK2 builds targeting
AARCH64.

Signed-off-by: Jose Marinho <jose.marinho@arm.com>
Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
Reviewed-by: Michael Kubacki <michael.kubacki@microsoft.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>