Migrate the chip power mode status to public ath_hal, rather than the
private per-chip HAL.

This allows the ah_osdep.[ch] code to check whether the power state is
valid for doing chip programming.

It should be a no-op for normal driver work but it does require a
clean kernel/module rebuild, as the size of HAL structures have changed.

Now, this doesn't track whether the hardware is ACTUALLY awake,
as NETWORK_SLEEP wakes the chip up for a short period when traffic
is received.  This doesn't actually set the power mode to AWAKE, so
we have to be careful about how we touch things.

But it's enough to start down the path of implementing station mode
chipset power savings, as a large part of the silliness is making
sure the chip is awake during periodic calibration / ANI and
random places where transmit may be occuring.  I'd rather not a repeat
of debugging power save on ath9k, where races with calibration
and transmit path stuff took a couple years to shake out.

Tested:

* AR5416, STA mode
Also tag the current HAL power mode in ar9300_set_power_mode().