ARM: dts: qcom-msm8974: Convert ADSP to a MMIO device

The cx-supply has been removed as it's supposed to be set on a
per-board basis.

Signed-off-by: Konrad Dybcio <konrad.dybcio@somainline.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20220415115633.575010-17-konrad.dybcio@somainline.org