drm/atomic-helpers: Update vblank timestamping constants
drm/atomic-helpers: Update vblank timestamping constants

The atomic helpers don't call drm_calc_timestamping_constants, which
is a regression compared to the crtc helpers. Fix this.

Noticed while reviewing i915 atomic patches from Maarten.

v2: Also check state->enable to avoid a warning in dmesg. Reported by
Maarten.

Cc: Maarten Lankhorst <743c2818a341d71b99ed2b566f9f80c2fc288f93@linux.intel.com>
Reviewed-by: Maarten Lankhorst <743c2818a341d71b99ed2b566f9f80c2fc288f93@linux.intel.com>
Signed-off-by: Daniel Vetter <c1b6782c4af8f0673da8923a0702a1832e5940f4@intel.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs