arm64: dts: qcom: msm8998: Fix compatible of scm node

The scm binding and driver was updated to rely on the fallback to the
default qcom,scm for any modern SoC and as such both are required. Add
the default compatible to make the scm instance probe.

Fixes: d850156a

 ("arm64: dts: qcom: msm8998: Add firmware node")
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>