Use single threaded work queue for hid_compat

I doubt HID really needs to scale over multiple CPUs. So only use a
single threaded workqueue for HID_COMPAT. This avoids some excessive
thread use on systems with a larger number of CPUs.
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>