net: dwc_eth_qos: Add Qcom ethernet driver glue layer

The Qualcom ETHQOS hardware supports an RGMII macro which needs to be
configured according to following link speeds:
- SPEED_1000
- SPEED_100
- SPEED_10

So add a corresponding glue driver to configure RGMII macro.

Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>