northbridge/intel: move mrccache.c of sandybridge + haswell to common

The sourcecode is 99% the same. Only two lines differ, but not
in functionality.
Also rename mrccache.c -> mrc_cache.c

Tested-on: boot + suspend/resume on x220

Change-Id: I36f79d066336f223b608c70c847ea6ea6e4ad287
Signed-off-by: Alexander Couzens <lynxis@fe80.eu>
Reviewed-on: https://review.coreboot.org/14007
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>

src/northbridge/intel/nehalem/Kconfig

@@ -22,6 +22,7 @@ config NORTHBRIDGE_INTEL_NEHALEM
 	select INTEL_EDID
 	select TSC_MONOTONIC_TIMER
 	select INTEL_GMA_ACPI
+	select NORTHBRIDGE_INTEL_COMMON_MRC_CACHE
 
 if NORTHBRIDGE_INTEL_NEHALEM