vidioc_enum_fmt_vid_overlay() did nothing but call
vidioc_enum_fmt_vid_cap(), so just make
saa7146_video_ioctl_ops.vidioc_enum_fmt_vid_overlay point to
vidioc_enum_fmt_vid_cap() and get ride of vidioc_enum_fmt_vid_overlay().

Have gparm use v4l2_video_std_frame_period to fill in the frame period
instead of just assuming PAL.
Signed-off-by: NTrent Piepho <xyzzy@speakeasy.org>
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>