The settings in GPR8 are dependent upon the particular layout of the
hardware platform.  As such, they should be configurable via the device
tree.

Look up PHY Tx driver settings from the device tree.  Fall back to the
original hard-coded values if they are not specified in the device tree.
Signed-off-by: NJustin Waters <justin.waters@timesys.com>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>
Acked-by: NLucas Stach <l.stach@pengutronix.de>