security/intel/txt: add missing cpu/x86/msr.h include

msr_t and a few other things used in here are defined in cpu/x86/msr.h,
so include it directly in this file.

Change-Id: I7a3299381ff54b7665620861dec60642f27bac8d
Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/56186
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Marshall Dawson <marshalldawson3rd@gmail.com>

src/security/intel/txt/common.c

@@ -6,6 +6,7 @@
 #include <cpu/x86/cr.h>
 #include <cpu/x86/lapic.h>
 #include <cpu/x86/mp.h>
+#include <cpu/x86/msr.h>
 #include <cpu/x86/mtrr.h>
 #include <lib.h>
 #include <smp/node.h>