x86 boot: x86_64 efi compiler warning fix

Fix a compiler warning.  Rather than always casting a u32 to a pointer
(which generates a warning on x86_64 systems) instead separate the
x86_32 and x86_64 assignments entirely with ifdefs.  Until other recent
changes to this code, it used to have x86_64 separated like this.

Signed-off-by: Paul Jackson <pj@sgi.com>
Cc: "Yinghai Lu" <yhlu.kernel@gmail.com>
Cc: "Jack Steiner" <steiner@sgi.com>
Cc: "Mike Travis" <travis@sgi.com>
Cc: "Huang
Cc: Ying" <ying.huang@intel.com>
Cc: "Andi Kleen" <andi@firstfloor.org>
Cc: "Andrew Morton" <akpm@linux-foundation.org>
Cc: Paul Jackson <pj@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>