net: qcom/emac: add ethtool support

Add support for some ethtool methods: get/set link settings, get/set
message level, get statistics, get link status, get ring params, get
pause params, and restart autonegotiation.

The code to collect the hardware statistics is moved into its own
function so that it can be used by "get statistics" method.

Signed-off-by: Timur Tabi <timur@codeaurora.org>
Signed-off-by: David S. Miller <davem@davemloft.net>