net: bcmgenet: move clk_wol management to bcmgenet_wol

The GENET_POWER_WOL_MAGIC power up and power down code configures
the device for WoL when suspending and disables the WoL logic when
resuming. It makes sense that this code should also manage the WoL
clocking.

This commit consolidates the logic and moves it earlier in the
resume sequence.

Since the clock is now only enabled if WoL is successfully entered
the wol_active flag is introduced to track that state to keep the
clock enables and disables balanced in case a suspend is aborted.
The MPD_EN hardware bit can't be used because it can be cleared
when the MAC is reset by a deep sleep.

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