spi: Migrate CONFIG_KIRKWOOD_SPI to Kconfig

Signed-off-by: Tuomas Tynkkynen <tuomas@tuxera.com>
diff --git a/configs/maxbcm_defconfig b/configs/maxbcm_defconfig
index 83fd4a4..b91c3ed 100644
--- a/configs/maxbcm_defconfig
+++ b/configs/maxbcm_defconfig
@@ -38,3 +38,4 @@
 CONFIG_DEBUG_UART_CLOCK=250000000
 CONFIG_DEBUG_UART_SHIFT=2
 CONFIG_SYS_NS16550=y
+CONFIG_KIRKWOOD_SPI=y