drm/i915/power: use intel_de_wait_for_clear() instead of wait_for()

Prefer the register read specific wait function over i915 wait_for_us().

The existing condition is quite complicated. Simplify by checking for
requesters first, and determine timeout based on that. Refresh
requesters in case of timeouts, should one have popped up during the
wait. The downside is that this does not cut the wait short if
requesters show up *during* the wait, but we're talking about 1 ms so
shouldn't be an issue.

v2: Refresh requesters only if there were none before (Imre)

Cc: Imre Deak <imre.deak@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Link: https://lore.kernel.org/r/20250626192632.2330349-1-jani.nikula@intel.com


Signed-off-by: Jani Nikula <jani.nikula@intel.com>