arm/efi: Allow invocation of arbitrary runtime services

efi_call_runtime() is provided for x86 to be able abstract mixed mode
support.  Provide this for ARM also so that common code work in mixed mode
also.

Suggested-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/1486380166-31868-3-git-send-email-ard.biesheuvel@linaro.org


Signed-off-by: Ingo Molnar <mingo@kernel.org>