drm/i915/dp: Refactor joiner max_bpp calculations into separate functions

drm/i915/dp: Refactor joiner max_bpp calculations into separate functions

Currently compressed max_bpp limitations for small joiner ram, big joiner
etc are intermingled. Seprate these limitations into separate functions.

v2: Use num_joined_pipes in small joiner ram helper and other minor
fixes. (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/20240930163549.416410-8-ankit.k.nautiyal@intel.com