net: phy: realtek: Disable clock on suspend

For PHYs that call rtl821x_probe() where an external clock can be
configured, make sure that the clock is disabled
when ->suspend() is called and enabled on resume.

The PHY_ALWAYS_CALL_SUSPEND is added to ensure that the suspend function
is actually always called.

Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: Detlev Casanova <detlev.casanova@collabora.com>
Signed-off-by: David S. Miller <davem@davemloft.net>