drm/i915: Set legacy properties when using legacy gamma set IOCTL. (v2)

The i915 driver is now using atomic properties and atomic commit
to handle the legacy set gamma IOCTL. However, if the driver is
configured without atomic (nuclear_pageflip = false), it won't
update the legacy properties for degamma_lut, gamma_lut and ctm
leaving them out of sync with the atomic version of the properties.

Until the driver is full atomic, make sure we update the non-atomic
version of the properties.

v2: Update the comment with a FIXME.  (Daniel)

v3: Update arguments of the gamma_set vfunc (Lionel)

v4: Fixed vfunc prototype (Lionel)

igt-testcase: kms_pipe_color / legacy-gamma-reset-pipeX
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: stable@vger.kernel.org #v4.7
Signed-off-by: Bob Paauwe <bob.j.paauwe@intel.com>
Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1468591142-2253-1-git-send-email-lionel.g.landwerlin@intel.com