net: systemport: fetch and use clock resources

We disable clocks shortly after probing the device to save as much power as
possible in case the interface is never used. When bcm_sysport_open() is
invoked, clocks are enabled, and disabled in bcm_sysport_stop().

A similar scheme is applied to the suspend/resume functions.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>