Document the qcom,qcm6490-idp and qcs6490-rb3gen2 boards.
qcm6490-idp based off qcm6490 SoC derived from sc7280 meant for
various form factor including IoT and qcs6490-rb3gen2 based off
qcs6490 SoC derivative of qcm6490 without internal modem.

Co-developed by: Naina Mehta <quic_nainmeht@quicinc.com>
Signed-off by: Naina Mehta <quic_nainmeht@quicinc.com>
Signed-off-by: Komal Bajaj <quic_kbajaj@quicinc.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20231129065816.26409-2-quic_kbajaj@quicinc.comSigned-off-by: Bjorn Andersson <andersson@kernel.org>