x86_64: Enable fp-reg promotion

Patch introduces 4 register XMM12-15 available for promotion of
fp virtual registers.

Change-Id: I3f89ad07fc8ae98b70f550eada09be7b693ffb67
Signed-off-by: Serguei Katkov <serguei.i.katkov@intel.com>
Signed-off-by: Chao-ying Fu <chao-ying.fu@intel.com>
17 files changed