spi: Migrate CONFIG_KIRKWOOD_SPI to Kconfig

Signed-off-by: Tuomas Tynkkynen <tuomas@tuxera.com>
diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
index 79cd54e..21dd6e0 100644
--- a/drivers/spi/Kconfig
+++ b/drivers/spi/Kconfig
@@ -257,6 +257,12 @@
 	  Enable the TI Quad-SPI (QSPI) driver for DRA7xx and AM43xx evms.
 	  This driver support spi flash single, quad and memory reads.
 
+config KIRKWOOD_SPI
+	bool "Marvell Kirkwood SPI Driver"
+	help
+	  Enable support for SPI on various Marvell SoCs, such as
+	  Kirkwood and Armada 375.
+
 config LPC32XX_SSP
 	bool "LPC32XX SPI Driver"
 	help