Input: sentelic - enabling absolute coordinates output for newer hardware

- Hooking multi-finger coordinates output with kernel multitouch library;
- Enabling absolute coordinates output for Cx+ hardware. The older hardware
  performs much better in relative mode; thus relative mode related code
  are preserved.

Part of the code is based on the work done by Oskari Saarenmaa <os@ohmu.fi>,
which was used to support the clickpad found on ASUS UX21/31 Ultrabook.
On the other hand, the FSP found on UX21/31 doesn't have hardware capability
register other than PnP ID, which means that we'll have to figure out an
alternative approach to identify such pad correctly; otherwise, blindly
adding INPUT_PROP_BUTTONPAD property may compatability issues amongst
existing FSPs.

Signed-off-by: Tai-hwa Liang <avatar@sentelic.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>