The driver should not immediately read bootloader status when in
Application Update Mode. The CHG line will assert when the device has made
a state transition and is ready to report a new status via i2c.

This change adds a wait for completion in mxt_check_bootloader, and changes
the mxt_interrupt handler to signal the completion.
Signed-off-by: NBenson Leung <bleung@chromium.org>
Signed-off-by: NDaniel Kurtz <djkurtz@chromium.org>
Signed-off-by: NNick Dyer <nick.dyer@itdev.co.uk>
Acked-by: NYufeng Shen <miletus@chromium.org>
Signed-off-by: NDmitry Torokhov <dmitry.torokhov@gmail.com>