RISC-V: KVM: Upgrade SBI spec version to v0.3

We upgrade SBI spec version implemented by KVM RISC-V to v0.3 so
that Guest kernel can probe and use SBI extensions added by the
SBI v0.3 specification.

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