ec/google/chromeec: add support for retrieving DRAM part number

The DRAM part number can be stored in the CBI data. Therefore, add
support for fetching the DRAM part number from CBI.

BUG=b:112203105
TEST=Fetched data from CBI on phaser during testing.

Change-Id: Ia721c01aab5848ff36e11792adf9c494aa25c01d
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/27945
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Justin TerAvest <teravest@chromium.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>

src/ec/google/chromeec/ec_commands.h

@@ -4780,6 +4780,7 @@ enum cbi_data_tag {
 	CBI_TAG_BOARD_VERSION = 0, /* uint16_t or uint8_t[] = {minor,major} */
 	CBI_TAG_OEM_ID = 1,        /* uint8_t */
 	CBI_TAG_SKU_ID = 2,        /* uint8_t */
+	CBI_TAG_DRAM_PART_NUM = 3, /* variable length ascii, nul terminated. */
 	CBI_TAG_COUNT,
 };