arm64: dts: qcom: sc7180: Add soc-specific qfprom compat string

Add the soc-specific compatible string so that it can be matched
more specifically now that the driver cares which SoC it's on.

Signed-off-by: Evan Green <evgreen@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20201028172737.v3.2.Ia3b68ac843df93c692627a3a92b947b3a5785863@changeid


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