vboot: Separate vboot from chromeos

VBOOT_VERIFY_FIRMWARE should be independent of CHROMEOS. This allows use
of verified boot library without having to stick to CHROMEOS.

BUG=chrome-os-partner:55639

Change-Id: Ia2c328712caedd230ab295b8a613e3c1ed1532d9
Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: https://review.coreboot.org/15867
Tested-by: build bot (Jenkins)
Reviewed-by: Duncan Laurie <dlaurie@chromium.org>
diff --git a/src/mainboard/google/purin/Kconfig b/src/mainboard/google/purin/Kconfig
index aca20e3..d415211 100644
--- a/src/mainboard/google/purin/Kconfig
+++ b/src/mainboard/google/purin/Kconfig
@@ -29,7 +29,7 @@
 	select SPI_ATOMIC_SEQUENCING
 
 config CHROMEOS
-	select CHROMEOS_VBNV_FLASH
+	select VBOOT_VBNV_FLASH
 
 config MAINBOARD_DIR
 	string