drm/amdkfd: Avoid name confusion involved in queue unmapping

When unmapping the queues from HW scheduler, there are two actions:
reset and preempt. So naming the variables with only preempt is
inapproriate.

For functions such as destroy_queues_cpsch, what they do actually is to
unmap the queues on HW scheduler rather than to destroy them. Change the
name to reflect that fact. On the other hand, there is already a function
called destroy_queue_cpsch() which exactly destroys a queue, and the name
is very close to destroy_queues_cpsch(), resulting in confusion.

Signed-off-by: Yong Zhao <yong.zhao@amd.com>
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Oded Gabbay <oded.gabbay@gmail.com>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>