Convert CONFIG_NAND_DAVINCI to Kconfig

This converts the following to Kconfig:
   CONFIG_NAND_DAVINCI

Signed-off-by: Adam Ford <aford173@gmail.com>
diff --git a/configs/ea20_defconfig b/configs/ea20_defconfig
index 497e551..43292a1 100644
--- a/configs/ea20_defconfig
+++ b/configs/ea20_defconfig
@@ -30,6 +30,8 @@
 CONFIG_CMD_UBI=y
 CONFIG_ENV_IS_IN_SPI_FLASH=y
 # CONFIG_MMC is not set
+CONFIG_NAND=y
+CONFIG_NAND_DAVINCI=y
 CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_STMICRO=y
 CONFIG_SYS_NS16550=y