cpu/x86: compile earlymtrr.c code for romstage as well

In order to make this work earlymtrr.c needed to be removed
from intel/truxton/romstage.c. It's not a ROMCC board so
there's no reason to be including .c files.

Change-Id: If4f5494a53773454b97b90fb856f7e52cadb3f44
Signed-off-by: Andrey Petrov <andrey.petrov@intel.com>
Reviewed-on: https://review.coreboot.org/14094
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>
Reviewed-by: Furquan Shaikh <furquan@google.com>

src/cpu/x86/mtrr/Makefile.inc

@@ -1 +1,2 @@
 ramstage-y += mtrr.c
+romstage-y += earlymtrr.c

src/mainboard/intel/truxton/romstage.c

@@ -26,7 +26,6 @@
 #include "southbridge/intel/i3100/early_lpc.c"
 #include <northbridge/intel/i3100/raminit_ep80579.h>
 #include <superio/intel/i3100/i3100.h>
-#include "cpu/x86/mtrr/earlymtrr.c"
 #include "lib/debug.c" // XXX
 #include <cpu/x86/bist.h>
 #include <spd.h>