platform: rzfive: Enable Andes PMU for RZ/Five

Enable Andes PMU extension support for RZ/Five.
We also staticize renesas_rzfive_early_init() as
it is not used outside of this unit.

Signed-off-by: Yu Chien Peter Lin <peterlin@andestech.com>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Tested-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Anup Patel <anup@brainfault.org>