ARM: dts: msm: add perf-events support for msm8994

Add the device definitions for the performance monitor
unit on msm8994. This enables the perf-events
subsystem.

Change-Id: Ia07e9dafdc4dc41a70d1d7c3b67f3238baa6ffcb
Signed-off-by: Neil Leeder <nleeder@codeaurora.org>