spi: Migrate CONFIG_MXC_SPI to Kconfig

Signed-off-by: Tuomas Tynkkynen <tuomas@tuxera.com>
diff --git a/configs/zc5601_defconfig b/configs/zc5601_defconfig
index 82ded3c..cd2f521 100644
--- a/configs/zc5601_defconfig
+++ b/configs/zc5601_defconfig
@@ -30,4 +30,5 @@
 CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_STMICRO=y
 CONFIG_PHYLIB=y
+CONFIG_MXC_SPI=y
 CONFIG_OF_LIBFDT=y