V4L/DVB (11194): pvrusb2: Implement mechanism to force a full sub-device update

When a pvrusb2 driver instance first initializes, we need to be sure
to send out a complete state update for everything to all attached
modules.  The old i2c layer did this by keeping a separate mask of
"stale" bits for each attached module - and setting that mask to all
stale when that module attaches.  But the new sub-device adaptation
I've implemented here no longer has per-module stale bits.  So instead
there's now a global "force dirty" bit that is set upon instance
initialization, before the sub-devices are attached.  After the first
update, this bit is cleared, allowing for normal update-on-dirty
behavior.  In this manner, we ensure that all sub-devices have been
properly synchronized at initialization.

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