dm9000 remove dead external phy support, gpio fix

dm9000 has code to detect and initialize external phy parts, but later
on in the code the part is forced to use the internal phy
unconditionally.  Remove the unused/untested code.

change the GPIO initialization so that only the GPIO used as an
internal phy reset (hardwired in the chip) is set as an output.  The
remaining GPIO need to be handled by board specific code to prevent
possible drive conflicts.  Set as inputs for safety.

replace a few magic numbers with defines

Signed-off-by: Andrew Dyer <adyer@righthandtech.com>
Signed-off-by: Ben Warren <biggerbadderben@gmail.com>