mb/google/octopus: Use DIMM_INFO_PART_NUMBER_SIZE for part_num_store

This change uses DIMM_INFO_PART_NUMBER_SIZE to decide the size of
part_num_store that holds the number of DRAM part. It ensures that
host advertises the supported size to read part number from the EC.

BUG=b:115697578

Change-Id: I8439a301fc037b0acdc8b1226ad04d2f363838ef
Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: https://review.coreboot.org/29241
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Justin TerAvest <teravest@chromium.org>
Reviewed-by: Karthik Ramasubramanian <kramasub@google.com>
Reviewed-by: Jett Rink <jettrink@chromium.org>

src/mainboard/google/octopus/romstage.c

@@ -17,6 +17,7 @@
 #include <boardid.h>
 #include <console/console.h>
 #include <ec/google/chromeec/ec.h>
+#include <memory_info.h>
 #include <soc/meminit.h>
 #include <soc/romstage.h>
 
@@ -33,7 +34,7 @@ static void save_dimm_info_by_sku_config(void)
 
 void mainboard_save_dimm_info(void)
 {
-	char part_num_store[32];
+	char part_num_store[DIMM_INFO_PART_NUMBER_SIZE];
 	const char *part_num = NULL;
 
 	if (!IS_ENABLED(CONFIG_DRAM_PART_NUM_IN_CBI)) {