ARM: dts: qcom: msm8226: Add PMU node

Enable perf events on MSM8226 devices by adding the PMU node.

Signed-off-by: Matti Lehtimäki <matti.lehtimaki@gmail.com>
Reviewed-by: Luca Weiss <luca@z3ntu.xyz>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230520121933.15533-3-matti.lehtimaki@gmail.com