RISC-V: KVM: Don't flush TLB when PTE is unchanged

RISC-V: KVM: Don't flush TLB when PTE is unchanged

The gstage_set_pte() and gstage_op_pte() should flush TLB only when
a leaf PTE changes so that unnecessary TLB flushes can be avoided.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Tested-by: Atish Patra <atishp@rivosinc.com>
Reviewed-by: Nutty Liu <liujingqi@lanxincomputing.com>
Link: https://lore.kernel.org/r/20250618113532.471448-6-apatel@ventanamicro.com
Signed-off-by: Anup Patel <anup@brainfault.org>