spi: Migrate CONFIG_MXC_SPI to Kconfig

Signed-off-by: Tuomas Tynkkynen <tuomas@tuxera.com>
diff --git a/configs/dms-ba16_defconfig b/configs/dms-ba16_defconfig
index eb39f04..454a7d4 100644
--- a/configs/dms-ba16_defconfig
+++ b/configs/dms-ba16_defconfig
@@ -32,6 +32,7 @@
 CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_STMICRO=y
 CONFIG_PHYLIB=y
+CONFIG_MXC_SPI=y
 CONFIG_USB=y
 CONFIG_USB_STORAGE=y
 CONFIG_USB_KEYBOARD=y