The DS4 motion sensors are currently mapped by the hid-core driver
to non-existing axes in between ABS_MISC and ABS_MT_SLOT, because
the device already exhausted ABS_X-ABS_RZ. For a part the mapping
by hid-core is accomplished by a fixup in hid-sony as the motion
axes actually use vendor specific usage pages.

This patch makes the DS4 use a separate input device for the motion
sensors and reports acceleration data through ABS_X-ABS_Z and
gyroscope data through ABS_RX-ABS_RZ. In addition it extends the
event spec to allow gyroscope data through ABS_RX-ABS_RZ when
INPUT_PROP_ACCELEROMETER is set. This change was suggested by
Peter Hutterer during a discussion on linux-input.

[jkosina@suse.cz: rebase onto slightly newer codebase]
Signed-off-by: Roderick Colenbrander <roderick.colenbrander@sony.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>