drm/amdkfd: Use wait_queue_t to implement event waiting

Use standard wait queues for waiting and waking up waiting threads
instead of inventing our own. We still have our own wait loop
because the HSA event semantics require the ability to have one
thread waiting on multiple wait queues (events) at the same time.

Signed-off-by: Kent Russell <kent.russell@amd.com>
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Acked-by: Oded Gabbay <oded.gabbay@gmail.com>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>