cpu/mtrr.h: Fix macro names for MTRR registers

We use UNDERSCORE_CASE. For the MTRR macros that refer to an MSR,
we also remove the _MSR suffix, as they are, by definition, MSRs.

Change-Id: Id4483a75d62cf1b478a9105ee98a8f55140ce0ef
Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Reviewed-on: http://review.coreboot.org/11761
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins)

src/soc/intel/skylake/cpu.c

@@ -467,6 +467,6 @@ int soc_skip_ucode_update(u32 current_patch_id, u32 new_patch_id)
 	 * MTRRCAP[12]. Check for this feature and avoid reloading the
 	 * same microcode during cpu initialization.
 	 */
-	msr = rdmsr(MTRRcap_MSR);
+	msr = rdmsr(MTRR_CAP_MSR);
 	return (msr.lo & PRMRR_SUPPORTED) && (current_patch_id == new_patch_id - 1);
 }