spi: Migrate CONFIG_MPC8XXX_SPI to Kconfig

Signed-off-by: Tuomas Tynkkynen <tuomas@tuxera.com>
diff --git a/configs/MPC8349EMDS_defconfig b/configs/MPC8349EMDS_defconfig
index 523b841..2132ee4 100644
--- a/configs/MPC8349EMDS_defconfig
+++ b/configs/MPC8349EMDS_defconfig
@@ -17,4 +17,5 @@
 CONFIG_PHYLIB=y
 # CONFIG_PCI is not set
 CONFIG_SYS_NS16550=y
+CONFIG_MPC8XXX_SPI=y
 CONFIG_OF_LIBFDT=y