google/*: Add MAINBOARD_HAS_CHROMEOS where appropriate

Some recently upstreamed boards are missing this flag

Change-Id: I89d73970f23eed6ea127e620c38f9687b2f5b048
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Reviewed-on: http://review.coreboot.org/9949
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

src/mainboard/google/purin/Kconfig

@@ -27,6 +27,7 @@ config BOARD_SPECIFIC_OPTIONS # dummy
 	select COMMON_CBFS_SPI_WRAPPER
 	select HAVE_HARD_RESET
 	select MAINBOARD_HAS_BOOTBLOCK_INIT
+	select MAINBOARD_HAS_CHROMEOS
 	select SOC_BROADCOM_CYGNUS
 	select SPI_FLASH
 	select SPI_FLASH_SPANSION