Enable GCC compilations to keep external symbols when generating a PRM module. 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>