V4L/DVB (6695): pvrusb2: Implement functions to pass descriptive hardware info

Implement additional pvrusb2 device info table entries for a device
identifier and a device description.  Export this information via the
driver's internal API.  Make this information available via the sysfs
driver interface.  Also propagate this information into the v4l2
capability structure.  An app can now retrieve and report a
descriptive string about the particular type of hardware device it is
operating.

Signed-off-by: Mike Isely <isely@pobox.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>