drm/i915: Reduce duplicated forcewake logic

Introduce a structure to track the individual forcewake domains and use
that to eliminate duplicate logic.

v2: - Rebase on latest dinq (Mika)
    - for_each_fw_domain macro (Mika)
    - Handle reset atomically, keeping the timer running (Mika)
    - for_each_fw_domain parameter ordering (Chris)
    - defer timer on new register access (Mika)

v3: - Fix forcewake_reset/get race by waiting pending timers

v4: - cond_resched and verbose warning on timer deletion (Chris)
    - need to run pending timers manually on reset

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> (v1)
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Acked-by: Deepak S <deepak.s@linux.intel.com> (v2)
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>