Integrate meta-seco-rockchip in oniro

    manifests/default.xml:      Add new project meta-seco-rockchip
    local.conf.sample:          Add seco-px30-d23 to MACHINE
    bblayers.conf.sample:       Add meta-seco-rockchip layer to BBLAYERS
    conf-notes.txt              Add seco-px30-d23 to supported machines
    machines-and-flavours.yaml  Add linux-seco-px30-d23 and linux-seco-px30-d23-extra jobs
    linux-flavour.rst:          Add seco-px30-d23 to supported machines
    machines-and-flavours.rst   Add linux-seco-px30-d23 job
    boards/index.rst            Add seco-px30-d23 to supported boards

    Add the seco-px30-d23.rst file representing the new Seco's
    JUNO board (SBC-D23) in the oniro project.

Signed-off-by: Natalia Kovalenko <waykovalenko@gmail.com>