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.h

@@ -74,6 +74,7 @@ int google_chromeec_reboot(int dev_idx, enum ec_reboot_cmd type, uint8_t flags);
  */
 int google_chromeec_cbi_get_oem_id(uint32_t *id);
 int google_chromeec_cbi_get_sku_id(uint32_t *id);
+int google_chromeec_cbi_get_dram_part_num(char *buf, size_t bufsize);
 
 /* MEC uses 0x800/0x804 as register/index pair, thus an 8-byte resource. */
 #define MEC_EMI_BASE		0x800