drm/i915/dsc: Add rc_range_parameter calculation for YCbCr420

Some rc_range_parameter calculations were missed for YCbCr420,
add them to calculate_rc_param()

--v2
-take into account the new formula to get bpp_i

--v4
-Fix range_bpg_offset formula for YCbCr420 bpp <= 16 [Ankit]

--v5
-Fix comment and mention use of DSC C Model [Ankit]

Cc: Vandita Kulkarni <vandita.kulkarni@intel.com>
Cc: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Cc: Uma Shankar <uma.shankar@intel.com>
Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230710162456.2736949-1-suraj.kandpal@intel.com