drm/i915/ddi: Simplify waiting for a port to get active/idle via DDI_BUF_CTL

When waiting for a port to get active/idle there is no point in the
complexity of specifying an exact timeout and for that the suitable wait
API instead of just using the maximum timeout. The sequence in
particular is not performance critical at all either and due to
scheduling it's not guaranteed anyhow how long the wait will last at the
given timescale. In the usual case where the wait succeeds the actual
time waited does not change with the increased timeout.

Simplify things accordingly, describing the bspec platform specific
timeouts in code comments.

v2: Clarify the rationale in the commit log. (Jani)

Cc: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Mika Kahola <mika.kahola@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250214142001.552916-8-imre.deak@intel.com