spi: Migrate CONFIG_KIRKWOOD_SPI to Kconfig

Signed-off-by: Tuomas Tynkkynen <tuomas@tuxera.com>
diff --git a/configs/db-88f6820-amc_defconfig b/configs/db-88f6820-amc_defconfig
index c48a780..29c9a39 100644
--- a/configs/db-88f6820-amc_defconfig
+++ b/configs/db-88f6820-amc_defconfig
@@ -54,6 +54,7 @@
 CONFIG_DEBUG_UART_CLOCK=200000000
 CONFIG_DEBUG_UART_SHIFT=2
 CONFIG_SYS_NS16550=y
+CONFIG_KIRKWOOD_SPI=y
 CONFIG_USB=y
 CONFIG_DM_USB=y
 CONFIG_USB_EHCI_HCD=y