Reduce default tap_min_queue size for Elan touchpads

Elan hw v.4 touchpads often sends touchpad release packet right after
touchpad touch one. Most probably this happens due to PS/2 limited bandwith.
Reducing of tap_min_queue size to 1 makes multifinger tap detection
more reliable in this case.

Reviewed by: gonzo
Approved by: gonzo (mentor)
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D10266