drm/i915: Use crtc_state->has_psr instead of CAN_PSR for pipe update

In commit "drm/i915: Wait for PSR exit before checking for vblank
evasion", the idea was to limit the PSR IDLE checks when PSR is
actually supported. While CAN_PSR does do that check, it doesn't
applies on a per-crtc basis. crtc_state->has_psr is a more granular
check that only applies to pipe(s) that have PSR enabled.

Without the has_psr check, we end up waiting on the eDP transcoder's
PSR_STATUS register irrespective of whether the pipe being updated is
driving it or not.

v2: Remove unnecessary parantheses, make checkpatch happy.

v3: Move the has_psr check to intel_psr_wait_for_idle and commit
    message changes (DK).

v4: Derive dev_priv from intel_crtc_state (DK)

v5: Commit message changes to reflect the HW behavior (DK)

Fixes: a6089879 ("drm/i915: Wait for PSR exit before checking for vblank evasion")
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Signed-off-by: Tarun Vyas <tarun.vyas@intel.com>
Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180712053323.26266-1-tarun.vyas@intel.com