arm64: dts: sc7180: Add unit name to soc node

This is just like commit a1875bf9 ("arm64: dts: qcom: sdm845: Add
unit name to soc node") but for sc7180.

For reference, the warning being fixed was:
  Warning (unit_address_vs_reg): /soc:
  node has a reg or ranges property, but no unit name

Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Fixes: 90db71e4 ("arm64: dts: sc7180: Add minimal dts/dtsi files for SC7180 soc")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20200304105638.1.I9ea0d337fcb927f52a28b20613b2377b6249c222@changeid


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>