drm/i915/dp: Move compressed bpp check with 420 format inside the helper

Move the check for limiting compressed bits_per_pixel for 420,422
formats in the helper to compute bits_per_pixel.

v2: Fix typo in commit message. (Ankit)

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230817142459.89764-3-ankit.k.nautiyal@intel.com