nb/intel/haswell/finalize.c: Lock down MC ARB register

The Haswell System Agent BIOS Spec revision 0.6.0 indicates this
register needs to be locked, and Broadwell already locks it.

Tested on Asrock B85M Pro4, still boots and register is locked.

Change-Id: Icdeb39e2fdde1403b6ab83faed214addca863f4b
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/46680
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/northbridge/intel/haswell/finalize.c

@@ -24,6 +24,7 @@ void intel_northbridge_haswell_finalize_smm(void)
 	MCHBAR32_OR(REQLIM, 1UL << 31);
 	MCHBAR32_OR(DMIVCLIM, 1UL << 31);
 	MCHBAR32_OR(CRDTLCK, 1 << 0);
+	MCHBAR32_OR(MCARBLCK, 1 << 0);
 
 	/* Memory Controller Lockdown */
 	MCHBAR8(MC_LOCK) = 0x8f;

src/northbridge/intel/haswell/registers/mchbar.h

@@ -47,5 +47,6 @@
 #define REQLIM			0x6800
 #define DMIVCLIM		0x7000
 #define CRDTLCK			0x77fc
+#define MCARBLCK		0x7ffc
 
 #endif /* __HASWELL_REGISTERS_MCHBAR_H__ */