Convert CONFIG_SYS_I2C_MXC et al to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_I2C_MXC
   CONFIG_SYS_I2C_MXC_I2C1
   CONFIG_SYS_I2C_MXC_I2C2
   CONFIG_SYS_I2C_MXC_I2C3
   CONFIG_SYS_I2C_MXC_I2C4

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/nitrogen6s_defconfig b/configs/nitrogen6s_defconfig
index 396ca91..878991c 100644
--- a/configs/nitrogen6s_defconfig
+++ b/configs/nitrogen6s_defconfig
@@ -10,6 +10,9 @@
 CONFIG_ENV_SECT_SIZE=0x2000
 CONFIG_MX6S=y
 CONFIG_TARGET_NITROGEN6X=y
+CONFIG_SYS_I2C_MXC_I2C1=y
+CONFIG_SYS_I2C_MXC_I2C2=y
+CONFIG_SYS_I2C_MXC_I2C3=y
 CONFIG_DM_GPIO=y
 CONFIG_DEFAULT_DEVICE_TREE="imx6dl-nitrogen6x"
 CONFIG_CMD_HDMIDETECT=y
@@ -52,6 +55,7 @@
 CONFIG_USB_FUNCTION_FASTBOOT=y
 CONFIG_FASTBOOT_BUF_ADDR=0x12000000
 CONFIG_SYS_I2C_LEGACY=y
+CONFIG_SYS_I2C_MXC=y
 CONFIG_FSL_USDHC=y
 CONFIG_MTD=y
 CONFIG_DM_SPI_FLASH=y