[PATCH 0/4 TRY#3] improve alternative instruction code and optimize get_cycles_sync

This series of patches extend the alternative instructions framework on
i386 and x86_64 architectures to support two alternative instruction
replacements. This code is used together with the introduction of the
X86_FEATURE_SYNC_RDTSC flag on i386 to simplify and optimize the
get_cycles_sync() function. The optimization changes this function to
use RDTSCP instead of CPUID;RDTSC if this instruction is available.
Don't use CPUID there is really important if the kernel runs as a KVM
guest, because this instruction is intercepted and causes an expensive
VMEXIT.

Changes to the previous submit:
 * rebased to current linus git tree
 * replaced RDTSCP usage in get_cycles_sync with the opcode to
   make it compile with older binutils

-- 
Joerg Roedel
Operating System Research Center
AMD Saxony LLC & Co. KG