touchpad_st: update touchpad hung detection logic
touchpad_st: update touchpad hung detection logic

When idle count does not change, reset the touchpad if there are no
fingers on touchpad.

BRANCH=nocturne
BUG=b:113315759
TEST=tested on whiskers
Signed-off-by: Wei-Han Chen <5413a119f383c3f4549c3ef659403f393bf06e9d@chromium.org>
Change-Id: I8336bac2b31963e4c2cb671ced8502e6b176424d
Reviewed-on: https://chromium-review.googlesource.com/1261615
Commit-Ready: ChromeOS CL Exonerator Bot <fa429e5907f00867f797423aea74327bb02c91b6@appspot.gserviceaccount.com>
Reviewed-by: Nicolas Boichat <f3daba1cdc403799935674d3cd4b0e5bd1804232@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec