drm/i915: Move vblank enable earlier and disable later

We changed to an interrupt based vblank wait (as opposed to polling)
in:
 commit 44bd93a3d367913d883be6abba9a6e51a53c4e90
 Author: Daniel Vetter <daniel.vetter@ffwll.ch>
 Date:   Fri Jul 25 23:36:44 2014 +0200

    drm/i915: Use generic vblank wait

However we already had vblank waits on the wrong side of
drm_vblank_{on,off}() calls due to various workarounds, so now we get
a warning more or less every time we do a modeset, and we fail to
wait for the vblank like we should.

Move the drm_vblank_{on,off}() calls back out from
intel_crtc_{enable,disable}_planes() so that all of these vblank waits
return to proper operation. Also move the cxsr wait a bit earlier so
that we can keep the encoder disable after we've turned off vblanks.
Moving stuff out from the plane enable/disable functions seems
preferrable to moving the workaround stuff in since the workarounds are
required only on specific platforms.

While at it switch over to the drm_crtc_ variants of the vblank on/off
functions.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=82525
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=82490


Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>