QBT1000: Add input device for home button

In order to support the fingerprint based home button sensor
feature, the QBT1000 driver creates an input device which
will be used by the user space daemon to send home button
down and up events.

Change-Id: Id3c81d350cbf12f74e20dc7594ab396afcc341c5
Signed-off-by: Lior Barenboim <liorb@codeaurora.org>
Acked-by:  <bpatel@qti.qualcomm.com>
Signed-off-by: Ian Maund <imaund@codeaurora.org>