arm64: dts: qcom: ipq8074: add SPMI bus

IPQ8074 uses SPMI for communication with the PMIC, so
since its already supported add the DT node for it.

Signed-off-by: Robert Marko <robimarko@gmail.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20210905165816.655275-1-robimarko@gmail.com