drm/i915/hdcp: use generic poll_timeout_us() instead of __wait_for()

drm/i915/hdcp: use generic poll_timeout_us() instead of __wait_for()

Prefer generic poll helpers over i915 custom helpers.

The functional change is losing the exponentially growing sleep of
__wait_for(), which used to be 1, 2, 4, ... 64, and 128 ms in this
particular case.

Use an arbitrary 100 ms sleep instead. The timeout remains at 5000 ms.

Cc: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Link: https://lore.kernel.org/r/bfc9f941ec1628830644f1419d606e3d085aaba0.1756383233.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>