CHROMIUM: Input: atmel_mxt_ts - move mxt_intialize

CHROMIUM: Input: atmel_mxt_ts - move mxt_intialize

Refactor only; no functional change.
This patch is in preparation for moving device creation and irq request
into mxt_initialize.  This will move all non-bootloader initialization
into a single function that can be called:
  a) on probe(), if device is using the APP i2c address
  b) after update_fw
  c) after updating device configuration

Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
BUG=chromium-os:11197
TEST=builds clean; no functional change

Change-Id: I66c23f5922e013edeb8caa75788931792c16d2d8
Reviewed-on: https://gerrit.chromium.org/gerrit/20849
Commit-Ready: Daniel Kurtz <djkurtz@chromium.org>
Reviewed-by: Daniel Kurtz <djkurtz@chromium.org>
Tested-by: Daniel Kurtz <djkurtz@chromium.org>