drm/i915/dp: Track the pipe and link bpp limits separately

drm/i915/dp: Track the pipe and link bpp limits separately

A follow-up patch will need to limit the output link bpp both in the
non-DSC and DSC configuration, so track the pipe and link bpp limits
separately in the link_config_limits struct.

Use .4 fixed point format for link bpp matching the 1/16 bpp granularity
in DSC mode and for now keep this limit matching the pipe bpp limit.

v2: (Jani)
- Add to_bpp_int(), to_bpp_x16() helpers instead of opencoding them.
- Rename link_config_limits::link.min/max_bpp to min/max_bpp_x16.

Cc: Jani Nikula <jani.nikula@linux.intel.com>
Reviewed-by: Luca Coelho <luciano.coelho@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230921195159.2646027-3-imre.deak@intel.com