XU control information is supposed to be entirely discoverable using
standard UVC queries. As some devices report bogus information (such as
reporting a read-only control as being read-write), add a fixup table
for XU controls.

This table can also be used to selectively disable requests supposed to
be supported by all XU controls (GET_MIN, GET_MAX, GET_DEF, GET_RES) but
not correctly (or at all) supported by the device.

The table currently disables GET_CUR on the Logitech motor control XU
pan/tilt controls.
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>