Calling input_mt_init_slots() copies ABS_MT_POSITION_X to ABS_X and
so on, but doing so before calling touchscreen_parse_properties()
leaves ABS_X min = max = 0 which may prompt an X server to ignore
the device.

To solve this problem, wait to call input_mt_init_slots() until all
absolute axis information has been resolved (whether that's through
device tree via touchscreen_parse_properties() or from reading from
the device directly).
Signed-off-by: Jeff LaBundy <jeff@labundy.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>