drm/i915/dp_mst: Move the check for dotclock at the end

drm/i915/dp_mst: Move the check for dotclock at the end

Refactor the mode_valid to have all joiner dependent stuff together and
place the check for dotclock limit at the very end.

This will help in the following refactor to iterate over the joiner
candidates and find the best joiner candidate that satisfy all checks
and limits.

v2: Update status to MODE_CLOCK_HIGH if max_dotclock check fails. (Imre)
v3: Drop redundant MODE_OK assignment and return. (Imre)

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Link: https://patch.msgid.link/20260202103731.357416-7-ankit.k.nautiyal@intel.com