Input: atmel_mxt_ts: Add a debugfs attribute to show all objects

The sysfs attribute show method (mxt_object_show) is limited to show
object information up to (PAGE_SIZE - 1) bytes. We need a way to get
the complete information of all objects. The object information can
be obtained from <debugfs-mount>/atmel_mxt_ts/object.

Change-Id: I92fff75b37ba0cba19b137460c2144fe847c6343
Signed-off-by: Jing Lin <jinglin@codeaurora.org>