standard-conformant bus_info

according to todays [1], bus_info must be prefixed by "platform:" by platform-devices
and "must simply count the devices controlled by the driver".

[1] http://linuxtv.org/downloads/v4l-dvb-apis/vidioc-querycap.html
since kernel-3.1 the cap version should be set by the v4l2 subsystem

and not by the driver
since kernel-3.3 we ought to set the device_caps field

if a device has multiple /dev/video* files, the "capabilities" should
be a union of all "device_caps".
since we only have a single device, we just equal the two
(with the notable exception of V4L2_CAP_DEVICE_CAPS which is only in
"capabilities")
pretend to not support {G,S,ENUM}_{IN,OUT}PUT depending on state

if we are ready_for_capture (that is, a producer is connected), we
don't support enumerating/getting/setting of OUTPUT at all.
similarily, if no producer is connected, we don't support
enumerating/getting/setting of INPUT at all.

oh, ENOTTY is used for "not-supporting at all".