x86: Make EFI RTC function depend on 32bit again

The EFI RTC functions are only available on 32 bit. commit 7bd867df
(x86: Move get/set_wallclock to x86_platform_ops) removed the 32bit
dependency which leads to boot crashes on 64bit EFI systems.

Add the dependency back.
Solves: http://bugzilla.kernel.org/show_bug.cgi?id=14466

Tested-by: Matthew Garrett <mjg59@srcf.ucam.org>
Signed-off-by: Feng Tang <feng.tang@intel.com>
LKML-Reference: <20091020125402.028d66d5@feng-desktop>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>