input: mc13xxx_ts: make press and release more robust

The touchscreen could sometimes seem to stop responding after a press
initiated by a light touch. This workaround continues polling the ts
for a while after the release is suspected to occur.

Signed-off-by: Marc Reilly <marc@cpdesign.com.au>
input: mx13xxx_ts: increase sensitivity

The contact pressure thresold is relaxed, and the delay between ADC
readings is increased. This seems to improve sensitivity for finger
presses.

Signed-off-by: Marc Reilly <marc@cpdesign.com.au>