Driver Input: FT5336 reports touch pressed on no touches

See https://github.com/zephyrproject-rtos/zephyr/discussions/69997



The driver thinks that when there are zero touches, the screen is
pressed. This changes it so zero touches mean the screen is not
pressed.

Also, multi-touch is now considered a single touch, and the
TOUCH_ID is checked so that only valid touches are registered.

Signed-off-by: Glenn Andrews <glenn.andrews.42@gmail.com>