[media] vivi: Teach it to tune FPS

[media] vivi: Teach it to tune FPS

I was testing my video-over-ethernet subsystem recently, and vivi
seemed to be perfect video source for testing when one don't have lots
of capture boards and cameras. Only its framerate was hardcoded to
NTSC's 30fps, while in my country we usually use PAL (25 fps) and I
needed that to precisely simulate bandwidth.
That's why here is this patch with ->enum_frameintervals() and
->{g,s}_parm() implemented as suggested by Hans Verkuil which passes
v4l2-compliance and manual testing through v4l2-ctl -P / -p <fps>.

Regarding newly introduced __get_format(u32 pixelformat) I decided not
to convert original get_format() to operate on fourcc codes, since >= 3
places in driver need to deal with v4l2_format and otherwise it won't be
handy.

[mchehab@redhat.com: Some CodingStyle fixes]

Signed-off-by: Kirill Smelkov <kirr@mns.spb.ru>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>