spi: Migrate CONFIG_MXC_SPI to Kconfig

Signed-off-by: Tuomas Tynkkynen <tuomas@tuxera.com>
diff --git a/configs/dms-ba16-1g_defconfig b/configs/dms-ba16-1g_defconfig
index d65b9a2..107f015 100644
--- a/configs/dms-ba16-1g_defconfig
+++ b/configs/dms-ba16-1g_defconfig
@@ -33,6 +33,7 @@
 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