drm/i915/dp: Introduce helper to check pixel rate against dotclock limits

drm/i915/dp: Introduce helper to check pixel rate against dotclock limits

Add intel_dp_dotclk_valid() helper, that checks the required pixel rate
against platform dotclock limit. With joined pipes the effective dotclock
limit depends upon the number of joined pipes.

Call the helper from the mode_valid phase and from the compute_config
phase where we need to check the limits for the given target clock for a
given joiner candidate.

v2: Rename the helper to intel_dp_dotclk_valid(). (Imre)

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Link: https://patch.msgid.link/20260202103731.357416-13-ankit.k.nautiyal@intel.com