drm/amdkfd: fix sysfs kobj leak

3 cases of kobj leak, which causes memory leak:

kobj_type must have release() method to free memory from release
callback. Don't need NULL default_attrs to init kobj.

sysfs files created under kobj_status should be removed with kobj_status
as parent kobject.

Remove queue sysfs files when releasing queue from process MMU notifier
release callback.

Signed-off-by: Philip Yang <Philip.Yang@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>