In the following patches we need to do context configuration which might
fail. Add new functions, cal_ctx_prepare and cal_ctx_unprepare, to
handle such configuration.

[hverkuil: fix spurious newline checkpatch warning]
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>