arm: mvebu: Use MVEBU_SPL_BOOT_DEVICE instead of SPL_BOOT_DEVICE

Update the way KWB_CFG_SEC_BOOT_DEV is determined to use
CONFIG_MVEBU_SPL_BOOT_DEVICE_{SPI,MMC} instead of
CONFIG_SPL_BOOT_DEVICE.

Signed-off-by: Chris Packham <judge.packham@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/arch/arm/mach-mvebu/Makefile b/arch/arm/mach-mvebu/Makefile
index 8bd2246..61eeb9c 100644
--- a/arch/arm/mach-mvebu/Makefile
+++ b/arch/arm/mach-mvebu/Makefile
@@ -65,10 +65,12 @@
 KWB_CFG_CSK_INDEX = $(CONFIG_SECURED_MODE_CSK_INDEX)
 
 KWB_REPLACE += SEC_BOOT_DEV
-KWB_CFG_SEC_BOOT_DEV=$(patsubst "%",%, \
-	$(if $(findstring BOOT_SPI_NOR_FLASH,$(CONFIG_SPL_BOOT_DEVICE)),0x34) \
-	$(if $(findstring BOOT_SDIO_MMC_CARD,$(CONFIG_SPL_BOOT_DEVICE)),0x31) \
-	)
+ifneq ($(CONFIG_MVEBU_SPL_BOOT_DEVICE_SPI),)
+	KWB_CFG_SEC_BOOT_DEV=0x34
+endif
+ifneq ($(CONFIG_MVEBU_SPL_BOOT_DEVICE_MMC),)
+	KWB_CFG_SEC_BOOT_DEV=0x31
+endif
 
 KWB_REPLACE += SEC_FUSE_DUMP
 KWB_CFG_SEC_FUSE_DUMP = a38x