mb/google/volteer: select GOOGLE_SMBIOS_MAINBOARD_VERSION

In order to use the function smbios_mainboard_version()
to query the board revision from the EC.
we need to select GOOGLE_SMBIOS_MAINBOARD_VERSION.

BUG=b:177818769
TEST=1. emerge-volteer coreboot chromeos-bootimage
     2. flash the image to the device and check board rev
        by using command `dmidecode -t 1 | grep Version`

Change-Id: I2474ee03845356d0775f6da25274f696ad33f935
Signed-off-by: Zhuohao Lee <zhuohao@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/49644
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>

src/mainboard/google/volteer/Kconfig

@@ -22,6 +22,7 @@ config BOARD_GOOGLE_BASEBOARD_VOLTEER
 	select EC_GOOGLE_CHROMEEC_LPC
 	select FW_CONFIG
 	select FW_CONFIG_SOURCE_CHROMEEC_CBI
+	select GOOGLE_SMBIOS_MAINBOARD_VERSION
 	select HAVE_ACPI_RESUME
 	select HAVE_ACPI_TABLES
 	select INTEL_LPSS_UART_FOR_CONSOLE