net: phy: meson-gxl: reuse functionality of the SMSC PHY driver

The Amlogic Meson internal PHY's have the same register layout as
certain SMSC PHY's (also for non-c22-standard registers). This seems
to be more than just coincidence. Apparently they also need the same
workaround for EDPD mode (energy detect power down). Therefore let's
reuse SMSC PHY driver functionality in the meson-gxl PHY driver.

Tested with a G12A internal PHY. I don't have GXL test hw,
therefore I replace only the callbacks that are identical in
the SMSC PHY driver.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>