dt-bindings: arm: qcom: document zoglin board

Zoglin is a Hoglin Chromebook with SPI Flash reduced from 64MB to 8MB.
Zoglin is identical to Hoglin except for the SPI Flash.
The actual SPI Flash is dynamically probed at and not specified in DTS.

Reviewed-by: Douglas Anderson <dianders@chromium.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bob Moragues <moragues@chromium.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20220728143215.v3.1.I5b9006878bdabd6493b866b46dbd6149968d545b@changeid