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/haswell/haswell.h

@@ -213,8 +213,6 @@ void dump_mem(unsigned start, unsigned end);
 void report_platform_info(void);
 #endif /* !__SMM__ */
 
-struct mrc_data_container;
-struct mrc_data_container *find_current_mrc_cache(void);
 #if !defined(__PRE_RAM__)
 #include "gma.h"
 int init_igd_opregion(igd_opregion_t *igd_opregion);