drm/i915/display: Drop check for doublescan mode in modevalid

Since the DP/HDMI connector do not set connector->doublescan_allowed,
the doublescan modes will get automatically filtered during
drm_helper_probe_single_connector_modes().

Therefore check for double scan modes is not required and is dropped
from modevalid functions for both DP and HDMI.

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Uma Shankar <uma.shankar@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221017143038.1748319-2-ankit.k.nautiyal@intel.com