RISC-V: KVM: Use NACL HFENCEs for KVM request based HFENCEs

RISC-V: KVM: Use NACL HFENCEs for KVM request based HFENCEs

When running under some other hypervisor, use SBI NACL based HFENCEs
for TLB shoot-down via KVM requests. This makes HFENCEs faster whenever
SBI nested acceleration is available.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Link: https://lore.kernel.org/r/20241020194734.58686-14-apatel@ventanamicro.com
Signed-off-by: Anup Patel <anup@brainfault.org>