drivers: ethernet: ksz8081: Fix reset times

500 ms reset time is only for software reset and comes from IEEE spec.
Datasheet mentions for hardware reset the assertion of the signal should
only need to be 500 us, and 100 us after deassert to wait to access
programming interface.

Also remove an unused macro.

Signed-off-by: Declan Snyder <declan.snyder@nxp.com>
(cherry picked from commit 96877736)