drm/i915/psr: Kill delays when activating psr back.

The immediate enabling was actually not an issue for the
HW perspective for core platforms that have HW tracking.
HW will wait few identical idle frames before transitioning
to actual psr active anyways.

Now that we removed VLV/CHV out of the picture completely
we can safely remove any delays.

Note that this patch also remove the delayed activation
on HSW and BDW introduced by commit 'd0ac896a
("drm/i915: Delay first PSR activation.")'. This was
introduced to fix a blank screen on VLV/CHV and also
masked some frozen screens on other core platforms.
Probably the same that we are now properly hunting and fixing.

v2:(DK): Remove unnecessary WARN_ONs and make some other
         VLV | CHV more readable.
v3: Do it regardless the timer rework.
v4: (DK/CI): Add VLV || CHV check on cancel work at psr_disable.
v5: Kill remaining items and fully rework activation functions.
v6: Rebase on top of VLV/CHV clean-up and keep the reactivation
    on a regular non-delayed work to avoid extra delays on exit
    calls and allow us to add few more safety checks before
    real activation.

Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180613192600.3955-1-rodrigo.vivi@intel.com