o Move the sysctls under debug.psm.* and hw.psm.* making them a bit
clearer and more consistent with other drivers.
o Remove the debug.psm_soft_timeout sysctl. It was introduced many
moons ago in r1.64 but never referenced anywhere.
o Introduce hw.psm.tap_threshold and hw.psm.tap_timeout to control
the behaviour of taps on touchpads. People might like to fiddle
with these if tapping seems to slow or too fast for them.
o Add debug.psm.loglevel as a tunable so that verbosity can be set
easily at boot-time (to watch probes and such) without having to
compile a kernel with options PSM_DEBUG=N.