drm/display/dp: Assume 8 bpc support when DSC is supported

As per DP v1.4, a DP DSC Sink device shall support 8bpc in DPCD 6Ah.
Apparently some panels that do support DSC, are not setting the bit for
8bpc.

So always assume 8bpc support by DSC decoder, when DSC is claimed to be
supported.

v2: Use helper to get check dsc support. (Ankit)
v3: Fix styling and other typos. (Jani)

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230824125121.840298-2-ankit.k.nautiyal@intel.com