input: touchpanel: fix the number of touch events detection

Focaltech controllers can reports the number of touch points by read
"TD_STATUS" register. Read this register to avoid always looping
through maximum number of touches supported.

Change-Id: I8ab111b56b2074cb52cb021d37e9e6505c8b7c72
Signed-off-by: Figo Wang <figow@codeaurora.org>
Signed-off-by: Bingzhe Cai <bingzhec@codeaurora.org>