drm/i915/backlight: Modify condition to use panel luminance

According to our internal spec we need to now check if both
panel luminance and smooth brightness are available in panel for
us to be able to change brightness using luminance value.

--v2
-Add Fixes tag [Ankit]

Fixes: 64481497 ("drm/i915/backlight: Check Luminance based brightness control for VESA")
Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>
Link: https://lore.kernel.org/r/20250411060235.2732060-3-suraj.kandpal@intel.com