spi: Migrate CONFIG_KIRKWOOD_SPI to Kconfig

Signed-off-by: Tuomas Tynkkynen <tuomas@tuxera.com>
diff --git a/configs/km_kirkwood_defconfig b/configs/km_kirkwood_defconfig
index d2d1fc1..2fe0058 100644
--- a/configs/km_kirkwood_defconfig
+++ b/configs/km_kirkwood_defconfig
@@ -30,5 +30,6 @@
 CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_STMICRO=y
 CONFIG_SYS_NS16550=y
+CONFIG_KIRKWOOD_SPI=y
 CONFIG_BCH=y
 CONFIG_OF_LIBFDT=y