V4L/DVB (6697): pvrusb2: Existence of Hauppauge ROM is a device-specific attribute

Arrange so that the pvrusb2 driver can optionally work without a
Hauppauge ROM being present - which is fairly important for devices
that happen to not come from Hauppauge.  The expected existence of a
Hauppauge ROM is now a device attribute.  The tuner type is now also a
device attribute, which is consulted if there is no ROM.

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