net: stmmac: SDx55 EMAC HW configuration changes

Add RGMII config and regulator support for EMAC HW configuration on SDx55.

Change-Id: I7b1cd3bcb7c78f5fa1c684d2523a41c51da72998
Acked-by: Suraj Jaiswal <jsuraj@codeaurora.org>
Acked-by: Nagarjuna Chaganti <nchagant@qti.qualcomm.com>
Signed-off-by: Sneh Shah <snehshah@codeaurora.org>