drivers: ksz8081: Some bug fixes & 25MHz RMII

- PHY can be set up as rmii but still use 25 MHz MDC, add DT property
  value for this case
- Fix KSZ8081 driver spamming phy status in debug level logging,
  and fix some other state/logging logic
- Fix PHY driver not rescheduling monitor work if first configuration
  fails, change code path to use goto for errors
- Handle case where some phys are not using the gpio pins in phy driver
  Make GPIO properties of ksz8081 phy optional since these hardware pins
  may be unused on some boards

Signed-off-by: Declan Snyder <declan.snyder@nxp.com>