Input: atmel_mxt_ts - wait for CHG assert in mxt_check_bootloader

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: Benson Leung <bleung@chromium.org>
Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
Signed-off-by: Nick Dyer <nick.dyer@itdev.co.uk>
Acked-by: Yufeng Shen <miletus@chromium.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>