x86/common.c: Make have_cpuid_p() a global function

Remove static declaration in have_cpuid_p() to make it a global function. The
function will be called in early loading microcode.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Link: http://lkml.kernel.org/r/1356075872-3054-4-git-send-email-fenghua.yu@intel.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>