[PATCH v3] Support for Alps SS5 touchpad

Hello all,

Here is the third iteration of my patchset adding support for the Alps SS5
touchpad used in the Dell Latitude E7470. The patch is largely unchanged except
for a reorganization of the DUALPOINT flag detection logic and the addition of
protocol documentation.

Thanks to everyone who has offered reviews so far.

Cheers,

- Ben



Changes:

v1:
 * Initial revision

v2:
 * Rework device detection
 * Fix contact release behavior of 1F events
 * Expose pressure of touchstick

v3:
 * Add protocol documentation
 * Move dualpoint detection into alps_set_protocol