Input: atmel_mxt_ts - initialise IRQ before probing

The maXTouch chips use the CHG line to generate status events in bootloader
mode, and during configuration download, before there is enough information
to configure the input device. Therefore set up the interrupt handler
earlier.

However, this introduces states where parts of the interrupt processing
must not run. Use data->object_table as a way to tell whether the chip
information is valid, and data->input_dev as a way to tell whether it is
valid to generate input report.

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