drm/i915: Enabled Modeset when HDR Infoframe changes

This patch enables modeset whenever HDR metadata
needs to be updated to sink.

v2: Addressed Shashank's review comments.

v3: Added Shashank's RB.

v4: Addressed Ville's review comments.

v5: Addressed Ville's review comments.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Uma Shankar <uma.shankar@intel.com>
Reviewed-by: Shashank Sharma <shashank.sharma@intel.com>
[mlankhorst: Fix up commit message, reorder]
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1558015817-12025-10-git-send-email-uma.shankar@intel.com