drm/i915/display: Use joined pipes in dsc helpers for slices, bpp

drm/i915/display: Use joined pipes in dsc helpers for slices, bpp

In preparation of ultrajoiner, use number of joined pipes in the dsc
helpers to compute dsc slices and max compressed bpp, instead of using
the joiner flag.

v2: Adjust the formulae to use num of pipes as 1 (no joiner) or 2
(bigjoiner). (Ankit)

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com> (v1)
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240916102836.2149012-5-ankit.k.nautiyal@intel.com