media: pixfmt-meta-rkisp1.rst: add description of rkisp1 metadata formats in pixfmt-meta-rkisp1.rst

The metadata formats V4L2_META_FMT_RK_ISP1_PARAMS,
V4L2_META_FMT_RK_ISP1_STAT_3A are currently described in
two files under
drivers/staging/media/rkisp1/Documentation/media/uapi/v4l

This patch moves the description to one file:
Documentation/userspace-api/media/v4l/pixfmt-meta-rkisp1.rst
The patch also extends the description and adds the rst file to
toctree.

Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld@collabora.com>
Acked-by: Helen Koike <helen.koike@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>