x86/efi: Update efi_thunk() to use the the arch_efi_call_virt*() macros

Currently, the efi_thunk macro has some semi-duplicated code in it that
can be replaced with the arch_efi_call_virt_setup/teardown macros. This
commit simply replaces the duplicated code with those macros.

Suggested-by: Matt Fleming <matt@codeblueprint.co.uk>
Signed-off-by: Alex Thorlton <athorlton@sgi.com>
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dimitri Sivanich <sivanich@sgi.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Roy Franz <roy.franz@linaro.org>
Cc: Russ Anderson <rja@sgi.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/1466839230-12781-7-git-send-email-matt@codeblueprint.co.uk
[ Renamed variables to the standard __ prefix. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>