msm: ultrasound: support multiple devices, conflicting with USF

The USF input device can have a number of devices,
conflicting with it.
The first registered device (primary) is real TSC device.
Optionally, later registered devices are simulated ones.
The input events from the multiple devices should be
controlled by USF.

Change-Id: I23855e665a3f884c6de55e34088c647b6670a10f
Signed-off-by: Baruch Eruchimovitch <baruche@codeaurora.org>