ARM: dts: msm: add DSU PMU support for sm6150

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: I2e9b0eaeac825e907a0025c0f2db39199e46eaa0
Signed-off-by: Srinivas Ramana <sramana@codeaurora.org>