net: fec: handle small PHY reset durations more precisely

Since msleep is based on jiffies the PHY reset could take longer
than expected. So use msleep for values greater than 20 msec otherwise
usleep_range.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Acked-by: Fugang Duan <fugang.duan@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>