kvm: move KVM_CAP_NR_MEMSLOTS to common code

All architectures except MIPS were defining it in the same way,
and memory slots are handled entirely by common code so there
is no point in keeping the definition per-architecture.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

virt/kvm/kvm_main.c

@@ -3063,6 +3063,8 @@ static long kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
 #endif
 	case KVM_CAP_MAX_VCPU_ID:
 		return KVM_MAX_VCPU_ID;
+	case KVM_CAP_NR_MEMSLOTS:
+		return KVM_USER_MEM_SLOTS;
 	default:
 		break;
 	}