arm64: dts: msm8996: Add #power-domain-cells property

Add #power-domain-cells property for both the gcc and mmcc
clock controller nodes as they both supports power domains (gdsc's)

Signed-off-by: Rajendra Nayak <rnayak@codeaurora.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>