drm/i915: Reduce PSR re-activation time for VLV/CHV.

With 'commit 30886c5a ("drm/i915: VLV/CHV PSR: Increase wait delay
 time before active PSR.")' we fixed a blank screen when first
activation was happening immediately after PSR being enabled.
There we gave more time for idleness by increasing the delay
between re-activating sequences.

However, commit "drm/i915: Delay first PSR activation."
delay the first activation in a better way keeping a good PSR
residency. So, we can now reduce the delay on re-enable.

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>