net: qcom/emac: add ethtool support for reading hardware registers

Implement the get_regs_len and get_regs ethtool methods.  The driver
returns the values of selected hardware registers.

The make the register offsets known to emac_ethtool, the the register
offset macros are all combined into one header file.  They were
inexplicably and arbitrarily split between two files.

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