include/cpu/x86/msr: introduce IA32_MC_*(x) macros

When accessing the MCA MSRs, the MCA bank number gets multiplied by 4
and added to the IA32_MC0_* define to get the MSR number. Add a macro
that already does this calculation to avoid open coding this repeatedly.

Change-Id: I2de753b8c8ac8dcff5a94d5bba43aa13bbf94b99
Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/56243
Reviewed-by: Raul Rangel <rrangel@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/security/intel/txt/common.c

@@ -483,7 +483,7 @@ bool intel_txt_prepare_txt_env(void)
 		*/
 		size_t max_mc_msr = mca_get_bank_count();
 		for (size_t i = 0; i < max_mc_msr; i++) {
-			msr = rdmsr(IA32_MC0_STATUS + 4 * i);
+			msr = rdmsr(IA32_MC_STATUS(i));
 			if (!(msr.hi & MCA_STATUS_HI_UC))
 				continue;