input: touchscreen: modify report event according to MT protocol B

Multi-touch(MT) protocol B use input_mt_report_slot_state()
instead of send ABS_MT_TRACKING_ID event directly, so modify
the driver to follow the protocol and remove redundant protocol
A code.

Change-Id: I542e61fabaaa04fcf5fb7e454e10599511f18e39
Signed-off-by: Bingzhe Cai <bingzhec@codeaurora.org>