drm/i915: VLV/CHV PSR Software timer mode

drm/i915: VLV/CHV PSR Software timer mode

This patch introduces exit/activate functions for PSR
on VLV+. Since on VLV+ HW cannot track frame updates and force PSR
exit let's use fully SW tracking available.

v2: Rebase over intel_psr.c;
    Remove Single Frame update transitioning from state 3 to 5 directly;
    Fake a software invalidation for sprites and cursor so we don't miss
    any screen update;

v3: As pointed out by Durgadoss msecs_to_jiffies used on wait_for only uses int,
    so let's use 1 instead. Althought the 1/4 of this is needed for the
    transition let's use 1 for simplicity;
    Also fix comments as suggested by Durgadoss

Cc: Durgadoss R <durgadoss.r@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Durgadoss R <durgadoss.r@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>