input: atmel_mxt_ts: Move the logic to save objects locally to a function

The Atmel touch driver reads information about a few objects at
initialization and saves them locally. Move this logic to its
own function.

Change-Id: I0f584ff5dcba6b713b3ac6b950ed64f3ad46faf1
Signed-off-by: Jing Lin <jinglin@codeaurora.org>