phylib: Support registering a bunch of drivers

If registering of one of them fails, all already registered drivers
of this module will be unregistered.

Use the new register/unregister functions in all drivers
registering more than one driver.

amd.c, realtek.c: Simplify: directly return registration result.

Tested with broadcom.c
All others compile-tested.

Signed-off-by: Christian Hohnstaedt <chohnstaedt@innominate.com>
Signed-off-by: David S. Miller <davem@davemloft.net>