ARM: dts: DRA7: Add PMU nodes

DRA74x and DRA72x family of processors vary slightly in the number
of CPUs. So, add different instances of PMU for each of these processor
groups. Further, since the interrupts bypass crossbar and are directly
connected to GIC, mark the dts nodes with relevant information.

Tested with perf utility.

Reviewed-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Lucas Weaver <l-weaver@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>