Convert CONFIG_DAVINCI_SPI to Kconfig

This converts the following to Kconfig:
   CONFIG_DAVINCI_SPI

Signed-off-by: Adam Ford <aford173@gmail.com>
diff --git a/configs/ea20_defconfig b/configs/ea20_defconfig
index eada103..abbb00a 100644
--- a/configs/ea20_defconfig
+++ b/configs/ea20_defconfig
@@ -32,5 +32,6 @@
 CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_STMICRO=y
 CONFIG_SYS_NS16550=y
+CONFIG_DAVINCI_SPI=y
 CONFIG_VIDEO=y
 # CONFIG_VIDEO_SW_CURSOR is not set