[media] em28xx: add support for Leadtek VC100 USB capture device

Leadtek VC100 is a simple USB capture stick, similar to
Yakumo Movie Mixer.

Signed-off-by: Witold Krecicki <wpk+lkml@culm.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>