V4L/DVB (13997): gspca_ov519: differentiate ov7620 and ov7620ae and fix 640x480 on the 7620

Michael Deegan <michael@ucc.gu.uwa.edu.au>, has reported issues with
using 640x480 mode on his ov518+ webcam. The fix for this breaks things
on my ov518+ cam (Trust 320 Sp@cecam), this patch thus adds differentiation
in the driver between the OV7620 sensor his cam has and the OV7620AE sensor
my cam has, and then only changes the init sequence for the ov518+ +
OV7620 combo which was not working for Michael.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>