arm64: dts: qcom: sc7280: Set modem FW path for Chrome OS boards

Specify the path of the modem FW for SC7280 Chrome OS boards in
the 'remoteproc_mpss' node.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220510104656.1.Id98b473e08c950f9a461826dde187ef7705a928c@changeid