ARM: dts: msm: add PMU support for sdm855

Add a device node to enable the armv8 PMU counters. This allows
perf subsystem to measure the hardware/raw performance events, such
as cycles count, instructions count, L1 misses and so on.

Change-Id: I11abc0c189de2c55dc80acc42af3bf4c3041eb0e
Signed-off-by: Raghavendra Rao Ananta <rananta@codeaurora.org>