x86, cpu: Fix X86_FEATURE_NOPL

ba0593bf cleared the aforementioned
cpuid bit only on 32-bit due to various problems with Virtual PC. This
somehow got lost during the 32- + 64-bit merge so restore the feature
bit on 64-bit. For that, set it explicitly for non-constant arguments of
cpu_has(). Update comment for future reference.

Signed-off-by: Borislav Petkov <bp@alien8.de>
LKML-Reference: <20101004073127.GA20305@liondog.tnic>
Cc: Ryan O'Neill <ryan@innosecc.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>