V4L/DVB (8822): gspca: Change some subdriver functions for suspend/resume.

- new function 'init' called on probe and resume
- remove the functions 'open' and 'closed'
- 'stopN' and 'stop0' are optional

Signed-off-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>