mb/google/octopus: Preserve MRC training data across firmware update

This change udpates FMAP to wrap MRC training data in RW_PRESERVE
section so that we don't lose the data when performing full firmware
updates on octopus.

BUG=b:117882029
TEST=Verified that chromeos-firmwareupdate doing full firmware update
preserves training data on octopus.

Change-Id: I5adb9bfa926327057b003360150685a8b4778c8c
Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: https://review.coreboot.org/29183
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Justin TerAvest <teravest@chromium.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
diff --git a/src/mainboard/google/octopus/chromeos.fmd b/src/mainboard/google/octopus/chromeos.fmd
index f601adc..6088f0d 100644
--- a/src/mainboard/google/octopus/chromeos.fmd
+++ b/src/mainboard/google/octopus/chromeos.fmd
@@ -12,10 +12,12 @@
 		}
 	}
 	MISC_RW@0x400000 0x30000 {
-		UNIFIED_MRC_CACHE@0x0 0x21000 {
-			RECOVERY_MRC_CACHE@0x0 0x10000
-			RW_MRC_CACHE@0x10000 0x10000
-			RW_VAR_MRC_CACHE@0x20000 0x1000
+		RW_PRESERVE {
+			UNIFIED_MRC_CACHE@0x0 0x21000 {
+				RECOVERY_MRC_CACHE@0x0 0x10000
+				RW_MRC_CACHE@0x10000 0x10000
+				RW_VAR_MRC_CACHE@0x20000 0x1000
+			}
 		}
 		RW_ELOG@0x21000 0x3000
 		RW_SHARED@0x24000 0x4000 {