x86: add common definitions for control registers

The access to control registers were scattered about.
Provide a single header file to provide the correct
access function and definitions.

BUG=chrome-os-partner:22991
BRANCH=None
TEST=Built and booted using this infrastructure. Also objdump'd the
     assembly to ensure consistency (objdump -d -r -S | grep xmm).

Change-Id: Iff7a043e4e5ba930a6a77f968f1fcc14784214e9
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/172641
Reviewed-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: http://review.coreboot.org/4873
Tested-by: build bot (Jenkins)
Reviewed-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>

src/arch/x86/include/arch/cpu.h

@@ -214,5 +214,6 @@ static inline void get_fms(struct cpuinfo_x86 *c, uint32_t tfms)
 #endif
 
 #define asmlinkage __attribute__((regparm(0)))
+#define alwaysinline inline __attribute__((always_inline))
 
 #endif /* ARCH_CPU_H */