touchpad: reduce button size, use physical sizes where possible

touchpad: reduce button size, use physical sizes where possible

The current 20% is excessive. On the t440s, the button size amounts to ~14mm
from the bottom. On the x220 it amounts to ~9mm, leaving only 31mm as actual
touchpad.

Reduce it to 15% instead, which amounts to 10.5mm on the t440 and 6mm on the
x220. Cap the button height further by making buttons a maximum height of
10mm, anything larger than that is excessive anyway.

Smaller buttons should be acceptable since we can rely on the bottom edge to
be a haptic feedback and thus a good hit-target, somewhat simliar to how
screen edges are good hit-targets.

The top software buttons stay the same size, but prefer a physical size of 6mm
instead (which is 1mm below the button marker line on the T440s). If no y
resolution is available, fall back to the 8% which is 5.6mm on the T440s.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>