dt-bindings: arm: qcom: Document MSM8939 SoC binding

Document the MSM8939 and supported boards in upstream Sony "Tulip" M4 Aqua
and Square APQ8039 T2.

MSM8939 is one of the older SoCs so we need to expand the list of
qcom,board-ids to allow for the bootloader DTS board-id matching
dependency.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230117024846.1367794-2-bryan.odonoghue@linaro.org