drm/i915/display: Simplify intel_joiner_num_pipes and its usage

drm/i915/display: Simplify intel_joiner_num_pipes and its usage

Currently intel_joiner_num_pipes is used to get num of pipes wrt num of
pipes joined. Simplify this by returning 1 when no joiner is used and
update the checks for no joiner case.

v2: Rename the function to intel_crtc_num_joined_pipes and use helper
intel_crtc_joined_pipe_mask. (Ville)

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240916102836.2149012-2-ankit.k.nautiyal@intel.com