cpuidle: riscv-sbi: Move sbi_cpuidle_init to arch_initcall

cpuidle: riscv-sbi: Move sbi_cpuidle_init to arch_initcall

Move the sbi_cpuidle_init to the arch_initcall to prevent the consumer
devices from being deferred.

Signed-off-by: Nick Hu <nick.hu@sifive.com>
Link: https://lore.kernel.org/lkml/CAKddAkAOUJSnM=Px-YO=U6pis_7mODHZbmYqcgEzXikriqYvXQ@mail.gmail.com/
Suggested-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/r/20240814054434.3563453-2-nick.hu@sifive.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>