media: allegro: start a GOP with an IDR frame

When creating a channel, freq_idr defines the number of frames between
IDR frames in the coded stream. In V4L2, the period between IDR frames
shall be taken from the GOP_SIZE control.

Set the IDR frame frequency equal to the GOP size and let every GOP
start with an IDR frame.

Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>