ARM: dts: msm: add DSU PMU support for sdm855

Add DT node to support the ARM DynamIQ Shared Unit (DSU) PMU.
This allows the perf subsystem clients to record the events
corresponding to the events related to L3 cache, snoop control
protocol, using its 32-bit counters.

Change-Id: Id38c3ece1d1e2533b53604e327254c07fa079755
Signed-off-by: Raghavendra Rao Ananta <rananta@codeaurora.org>