hw/riscv: virt: Fix riscv,pmu DT node path

hw/riscv: virt: Fix riscv,pmu DT node path

On a dtb dumped from the virt machine, dt-validate complains:
soc: pmu: {'riscv,event-to-mhpmcounters': [[1, 1, 524281], [2, 2, 524284], [65561, 65561, 524280], [65563, 65563, 524280], [65569, 65569, 524280]], 'compatible': ['riscv,pmu']} should not be valid under {'type': 'object'}
        from schema $id: http://devicetree.org/schemas/simple-bus.yaml#
That's pretty cryptic, but running the dtb back through dtc produces
something a lot more reasonable:
Warning (simple_bus_reg): /soc/pmu: missing or empty reg/ranges property

Moving the riscv,pmu node out of the soc bus solves the problem.

Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Message-ID: <20230727-groom-decline-2c57ce42841c@spud>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>