Convert CONFIG_SYS_I2C_DAVINCI to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_I2C_DAVINCI

Signed-off-by: Adam Ford <aford173@gmail.com>
diff --git a/configs/ea20_defconfig b/configs/ea20_defconfig
index c71594c..5dad8ef 100644
--- a/configs/ea20_defconfig
+++ b/configs/ea20_defconfig
@@ -31,6 +31,7 @@
 CONFIG_CMD_UBI=y
 CONFIG_ENV_IS_IN_SPI_FLASH=y
 CONFIG_DA8XX_GPIO=y
+CONFIG_SYS_I2C_DAVINCI=y
 # CONFIG_MMC is not set
 CONFIG_NAND=y
 CONFIG_NAND_DAVINCI=y