dt2w: Add an option to disable d2tw when the power button is used

This patch adds the variable doubletap_pwrkey_suspend to prevent the
touch device from staying enabled when the power button is used.

It has been inspired by the implementation for the Nexus 5 (Hammerhead)
by "flar2" <asegaert@gmail.com> and "showp1984" <showp1984@gmail.com>.

Signed-off-by: Mikael Berthe <mikael@lilotux.net>
dt2w: Restrict the touchscreen area used to wake up the device

Only the bottom area of the screen can be "double-tapped" to wake up the
device; this should reduce false positives.
Left and right margins are excluded as well.

Signed-off-by: Mikael Berthe <mikael@lilotux.net>
dt2w: Add option to use the whole screen for dt2w

This patch adds the /sys entry "doubletap_full_window".

When its value is true, the whole touchscreen can be used to wake up the
device.

Signed-off-by: Mikael Berthe <mikael@lilotux.net>