drm/i915: Move vblank wait determination to 'check' phase

Determining whether we'll need to wait for vblanks is something we
should determine during the atomic 'check' phase, not the 'commit'
phase.  Note that we only set these bits in the branch of 'check' where
intel_crtc->active is true so that we don't try to wait on a disabled
CRTC.

The whole 'wait for vblank after update' flag should go away in the
future, once we start handling watermarks in a proper atomic manner.

This regression has been introduced in

commit 2fdd7def16dd7580f297827930126c16b152ec11
Author: Matt Roper <matthew.d.roper@intel.com>
Date:   Wed Mar 4 10:49:04 2015 -0800
    drm/i915: Don't clobber plane state on internal disables

Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Root-cause-analysis-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=89550


Testcase: igt/pm_rpm/legacy-planes
Testcase: igt/pm_rpm/legacy-planes-dpms
Testcase: igt/pm_rpm/universal-planes
Testcase: igt/pm_rpm/universal-planes-dpms
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Tested-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>