RISC-V: KVM: Implement SBI STA extension

Add a select SCHED_INFO to the KVM config in order to get run_delay
info. Then implement SBI STA's set-steal-time-shmem function and
kvm_riscv_vcpu_record_steal_time() to provide the steal-time info
to guests.

Reviewed-by: Anup Patel <anup@brainfault.org>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
Signed-off-by: Anup Patel <anup@brainfault.org>