drm/i915/cx0: Replace XELPDP_PORT_POWERDOWN_UPDATE_TIMEOUT_US with XELPDP_PORT_POWERD...

drm/i915/cx0: Replace XELPDP_PORT_POWERDOWN_UPDATE_TIMEOUT_US with XELPDP_PORT_POWERDOWN_UPDATE_TIMEOUT_MS

There was a completely unjustified change to the cx0 powerdown
timeout, and the way it was done now prevents future conversion
to poll_timeout_us().

Assuming there was some reason the bigger timeout let's nuke
the old short timeout (XELPDP_PORT_POWERDOWN_UPDATE_TIMEOUT_US)
nd replace it with the bigger timeout
(XELPDP_PORT_POWERDOWN_UPDATE_TIMEOUT_MS).

For consistency with intel_wait_for_register() we'll stick to the
default 2 usec for the fast timeout.

v2: Go for the longer (ms) timeout in case it actually matters
v3: Note the defaullt 2 usec fast timeout (Jani)

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patch.msgid.link/20251106152049.21115-5-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>