spi: Migrate CONFIG_MXC_SPI to Kconfig

Signed-off-by: Tuomas Tynkkynen <tuomas@tuxera.com>
diff --git a/configs/aristainetos_defconfig b/configs/aristainetos_defconfig
index df15fba..41b57bd 100644
--- a/configs/aristainetos_defconfig
+++ b/configs/aristainetos_defconfig
@@ -39,6 +39,7 @@
 CONFIG_MTD_UBI_FASTMAP_AUTOCONVERT=1
 CONFIG_PHYLIB=y
 CONFIG_PHY_MICREL=y
+CONFIG_MXC_SPI=y
 CONFIG_USB=y
 CONFIG_USB_STORAGE=y
 CONFIG_VIDEO=y