nitrogen6x: convert to DM_I2C and DM_SERIAL

Rework to remove use of legacy I2C API. Also switch
to DM_SERIAL to avoid board removal warning.

Signed-off-by: Anatolij Gustschin <agust@denx.de>
Cc: Troy Kisky <troy.kisky@boundarydevices.com>
diff --git a/configs/nitrogen6dl_defconfig b/configs/nitrogen6dl_defconfig
index 6a0f48a..c2566c9 100644
--- a/configs/nitrogen6dl_defconfig
+++ b/configs/nitrogen6dl_defconfig
@@ -11,9 +11,6 @@
 CONFIG_IMX_CONFIG="board/boundary/nitrogen6x/nitrogen6dl.cfg"
 CONFIG_MX6DL=y
 CONFIG_TARGET_NITROGEN6X=y
-CONFIG_SYS_I2C_MXC_I2C1=y
-CONFIG_SYS_I2C_MXC_I2C2=y
-CONFIG_SYS_I2C_MXC_I2C3=y
 CONFIG_DDR_MB=1024
 CONFIG_DM_GPIO=y
 CONFIG_DEFAULT_DEVICE_TREE="imx6dl-nitrogen6x"
@@ -61,7 +58,7 @@
 CONFIG_BOUNCE_BUFFER=y
 CONFIG_USB_FUNCTION_FASTBOOT=y
 CONFIG_FASTBOOT_BUF_ADDR=0x12000000
-CONFIG_SYS_I2C_LEGACY=y
+CONFIG_DM_I2C=y
 CONFIG_SYS_I2C_MXC=y
 CONFIG_FSL_USDHC=y
 CONFIG_MTD=y
@@ -74,6 +71,8 @@
 CONFIG_MII=y
 CONFIG_PINCTRL=y
 CONFIG_PINCTRL_IMX6=y
+CONFIG_SPECIFY_CONSOLE_INDEX=y
+CONFIG_DM_SERIAL=y
 CONFIG_MXC_UART=y
 CONFIG_SPI=y
 CONFIG_DM_SPI=y