KVM: X86/MMU: Add sp_has_gptes()

Add sp_has_gptes() which equals to !sp->role.direct currently.

Shadow page having gptes needs to be write-protected, accounted and
responded to kvm_mmu_pte_write().

Use it in these places to replace !sp->role.direct and rename
for_each_gfn_indirect_valid_sp.

Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Message-Id: <20220420131204.2850-2-jiangshanlai@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>