arm64: dts: qcom: Replace PMU compatible with a53 specific one

The PMU on msm8916 is for the cortex-a53 type CPU. Update the
compatible to the more specific one so we can get the a53
specific events out of the PMU.

Signed-off-by: Stephen Boyd <stephen.boyd@linaro.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>