mrc: Add support for separate training cache in recovery mode

1. Re-factor MRC cache driver to properly select RW_MRC_CACHE or
RECOVERY_MRC_CACHE based on the boot mode.
 - If normal mode boot, use RW_MRC_CACHE, if available.
 - If recovery mode boot:
    - Retrain memory if RECOVERY_MRC_CACHE not present, or recovery is
    requested explicity with retrain memory request.
    - Use RECOVERY_MRC_CACHE otherwise.
2. Protect RW and RECOVERY mrc caches in recovery and non-recovery boot
modes. Check if both are present under one unified region and protect
that region as a whole. Else try protecting individual regions.
3. Update training data in appropriate cache:
 - Use RW_MRC_CACHE if normal mode.
 - Use RECOVERY_MRC_CACHE if present in recovery mode. Else use
 RW_MRC_CACHE.
4. Add proper debug logs to indicate which training data cache is used
at any point.

BUG=chrome-os-partner:59352
BRANCH=None
TEST=Verified that correct cache is used in both normal and recovery
mode on reef.

Change-Id: Ie79737a1450bd1ff71543e44a5a3e16950e70fb3
Signed-off-by: Furquan Shaikh <furquan@chromium.org>
Reviewed-on: https://review.coreboot.org/17242
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/include/elog.h

@@ -152,6 +152,7 @@ struct elog_event_data_me_extended {
 /* Memory Cache Update */
 #define ELOG_TYPE_MEM_CACHE_UPDATE        0xaa
 #define  ELOG_MEM_CACHE_UPDATE_SLOT_NORMAL    0
+#define  ELOG_MEM_CACHE_UPDATE_SLOT_RECOVERY  1
 #define  ELOG_MEM_CACHE_UPDATE_STATUS_SUCCESS 0
 #define  ELOG_MEM_CACHE_UPDATE_STATUS_FAIL    1
 struct elog_event_mem_cache_update {