V4L/DVB (6692): pvrusb2: Centralize device specific attributes into a single place

The pvrusb2 driver currently supports two variants of the Hauppauge
PVR USB2.  However there are other hardware types potentially
supportable, but the driver at the moment is not structured to make it
easy to describe these minor variations.  This changeset is the first
set of changes to make such additional device support possible.
Device attributes are held in several tables all contained within
pvrusb2-devattr.c; all other device-specific driver behavior now
derives from these tables.

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