net: stmmac: Add support for SM8150

This adds compatible, POR config & driver data for ethernet controller
found in SM8150 SoC.

Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Vinod Koul <vkoul@kernel.org>
[bhsharma: Massage the commit log and other cosmetic changes]
Signed-off-by: Bhupesh Sharma <bhupesh.sharma@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>