KVM: x86/mmu: Replace vcpu with kvm in kvm_mmu_alloc_shadow_page()

The vcpu pointer in kvm_mmu_alloc_shadow_page() is only used to get the
kvm pointer. So drop the vcpu pointer and just pass in the kvm pointer.

No functional change intended.

Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20220516232138.1783324-12-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>