[media] media: Add stk1160 new driver (easycap replacement)

[media] media: Add stk1160 new driver (easycap replacement)

This driver adds support for stk1160 usb bridge as used in some
video/audio usb capture devices.
It is a complete rewrite of staging/media/easycap driver and
it's meant as a replacement.

As stk1160 allows communication with an ac97 codec chip, this
driver allows to register a control-only sound card to allow the user
to access ac97 controls.

Two devices have been used for testing:
* 1-cvbs video and 1-audio ac97 input,
* 4-cvbs inputs
Both of these devices reports with the same id [05e1:0408],
so the driver tries to support a superset of the capabilities.

By using keep_buffers module parameter it's possible to prevent
the driver from releasing urb buffers when streaming is stopped.
The usage of this parameter can avoid memory fragmentation that may
cause the driver to stop working on low memory systems.
A similar mechanism is implemented in em28xx driver (see commit 86d38d).

Signed-off-by: Ezequiel Garcia <elezegarcia@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>