riscv: export cpu/freq invariant to scheduler

riscv: export cpu/freq invariant to scheduler

RISC-V now manages CPU topology using arch_topology which provides
CPU capacity and frequency related interfaces to access the cpu/freq
invariant in possible heterogeneous or DVFS-enabled platforms.

Here adds topology.h file to export the arch_topology interfaces for
replacing the scheduler's constant-based cpu/freq invariant accounting.

Signed-off-by: Song Shuai <suagrfillet@gmail.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Ley Foon Tan <lftan@kernel.org>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230323123924.3032174-1-suagrfillet@gmail.com
[Palmer: Fix the whitespace issues.]
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>