nb/intel/x4x: Use SPI flash to cache raminit results

Stores information obtained from decoding dimms and receive enable
results for future use.

Depreciates using rtc nvram to store receive enable settings.

A notable change is that receive enable results are always reused, not
just on a resume from S3.

This requires cbmem to be initialized a bit earlier, right after the
raminit finished to be able to add the sysinfo struct to cbmem which
gets cached to the SPI flash in ramstage.

TESTED on Intel DG43GT with W25Q128.V. With 4 ddr2 dimms time in
raminit goes from 133,857ms (using i2c block read to fetch SPD) to
21,071ms for cached results.

Change-Id: I042dc5c52615d40781d9ef7ecd657ad0bf3ed08f
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/21677
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
diff --git a/src/northbridge/intel/x4x/Kconfig b/src/northbridge/intel/x4x/Kconfig
index 9239637..d9dbdc9 100644
--- a/src/northbridge/intel/x4x/Kconfig
+++ b/src/northbridge/intel/x4x/Kconfig
@@ -28,6 +28,7 @@
 	select RELOCATABLE_RAMSTAGE
 	select HAVE_LINEAR_FRAMEBUFFER if MAINBOARD_DO_NATIVE_VGA_INIT
 	select HAVE_VGA_TEXT_FRAMEBUFFER if MAINBOARD_DO_NATIVE_VGA_INIT
+	select CACHE_MRC_SETTINGS
 
 config CBFS_SIZE
 	hex