intel/amenia: set default value for BOOT_MEDIA_SPI_BUS

BUG=chrome-os-partner:51844
TEST=Boot to chrome

Change-Id: I60d411482812d98cb8dd11d66b0fc96ea9bae895
Signed-off-by: Bora Guvendik <bora.guvendik@intel.com>
Reviewed-on: https://review.coreboot.org/16134
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>

src/mainboard/intel/amenia/Kconfig

@@ -14,6 +14,10 @@ config BOARD_SPECIFIC_OPTIONS
 	select SYSTEM_TYPE_LAPTOP
 	select TPM_ON_FAST_SPI
 
+config BOOT_MEDIA_SPI_BUS
+	int
+	default 0
+
 config CHROMEOS
 	select LID_SWITCH