ARM: imx6: DHCOM i.MX6 PDK: Switch to DM for I2C

This patch enables DM I2C for DHCOM i.MX6 PDK2 boards and
removes non DM I2C code. The I2C EEPROM with ethaddr (MAC)
is defined in the device tree. Use UCLASS_I2C_EEPROM
to find the device by fixed hardware path and read the ethaddr.

Tested with DHCOM i.MX6dl and DHCOM i.MX6q.

Signed-off-by: Ludwig Zenz <lzenz@dh-electronics.com>
Reviewed-by: Marek Vasut <marex@denx.de>