We can use sleeping functions when reading and writing the
PHY registers, so let us sleep instead of busy waiting for
the PHY.

Note, this also fixes a bug reading the PHY where only 100uS
was being used instead of 150uS
Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>