HID: sony: Report DS4 motion sensors through a separate device

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>

Documentation/input/event-codes.txt

@@ -301,7 +301,10 @@ them as any other INPUT_PROP_BUTTONPAD device.
 INPUT_PROP_ACCELEROMETER
 -------------------------
 Directional axes on this device (absolute and/or relative x, y, z) represent
-accelerometer data. All other axes retain their meaning. A device must not mix
+accelerometer data. Some devices also report gyroscope data, which devices
+can report through the rotational axes (absolute and/or relative rx, ry, rz).
+
+All other axes retain their meaning. A device must not mix
 regular directional axes and accelerometer axes on the same event node.
 
 Guidelines:

include/uapi/linux/input.h

@@ -61,9 +61,14 @@ struct input_id {
  * Note that input core does not clamp reported values to the
  * [minimum, maximum] limits, such task is left to userspace.
  *
- * Resolution for main axes (ABS_X, ABS_Y, ABS_Z) is reported in
- * units per millimeter (units/mm), resolution for rotational axes
- * (ABS_RX, ABS_RY, ABS_RZ) is reported in units per radian.
+ * The default resolution for main axes (ABS_X, ABS_Y, ABS_Z)
+ * is reported in units per millimeter (units/mm), resolution
+ * for rotational axes (ABS_RX, ABS_RY, ABS_RZ) is reported
+ * in units per radian.
+ * When INPUT_PROP_ACCELEROMETER is set the resolution changes.
+ * The main axes (ABS_X, ABS_Y, ABS_Z) are then reported in
+ * in units per g (units/g) and in units per degree per second
+ * (units/deg/s) for rotational axes (ABS_RX, ABS_RY, ABS_RZ).
  */
 struct input_absinfo {
 	__s32 value;