ENGR00227890 ts: fix elan touch screen gets no response upon suspend/resume

ENGR00227890 ts: fix elan touch screen gets no response upon suspend/resume

To reproduce:
1. let system enter suspend mode
2. touch the screen
3. after the system resumes, touch screen does not respond again.

The cause:
The touch screen interrupt is triggered by falling edge. During suspend stage,
once the screen has ever been touched, then the interrupt line will be always
pulled low. Since elan ts chip is always powered on and the interrupt gets no
chance to be handled during suspend stage, the interrupt line can not recover
to high to detect a new one.

Workaround:
Read out the pending data to make the touch screen come back alive.

Signed-off-by: LiGang <b41990@freescale.com>
Signed-off-by: Robby Cai <R63905@freescale.com>