Add delay to Octeon MDIO access routines.

Prevent saturattion of the bus by constant polling which in
extreme cases can cause interface lockup. This makes FreeBSD
match similar case in the executive.
Fix RTC clock writes on many Octeon boards.

The struct clocktime uses 0-based week day number, so back out part of
r229161 by gonzo, which actually broke the RTC clock writes on Sundays.