x86: kconfig: Let board select SPI flash

Only a specific type of SPI flash exists on a board, having board
Kconfig to select the SPI flash seems to make more sense. Other
flash types are not necessary except coreboot, which implies all
available flash drivers there.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/board/advantech/som-db5800-som-6867/Kconfig b/board/advantech/som-db5800-som-6867/Kconfig
index 945aa43..fac562a 100644
--- a/board/advantech/som-db5800-som-6867/Kconfig
+++ b/board/advantech/som-db5800-som-6867/Kconfig
@@ -22,6 +22,7 @@
 	select INTEL_BAYTRAIL
 	select BOARD_ROMSIZE_KB_8192
 	select BOARD_EARLY_INIT_F
+	select SPI_FLASH_MACRONIX
 
 config PCIE_ECAM_BASE
 	default 0xe0000000