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 <[e-mail]>

Documentation/virtual/kvm/api.txt

···
 This ioctl allows the user to create, modify or delete a guest physical
 memory slot.  Bits 0-15 of "slot" specify the slot id and this value
 should be less than the maximum number of user memory slots supported per
-VM.  The maximum allowed slots can be queried using KVM_CAP_NR_MEMSLOTS,
-if this capability is supported by the architecture.  Slots may not
-overlap in guest physical address space.
+VM.  The maximum allowed slots can be queried using KVM_CAP_NR_MEMSLOTS.
+Slots may not overlap in guest physical address space.
 
 If KVM_CAP_MULTI_ADDRESS_SPACE is available, bits 16-31 of "slot"
 specifies the address space which is being modified.  They must be

arch/powerpc/kvm/powerpc.c

···
 		else
 			r = num_online_cpus();
 		break;
-	case KVM_CAP_NR_MEMSLOTS:
-		r = KVM_USER_MEM_SLOTS;
-		break;
 	case KVM_CAP_MAX_VCPUS:
 		r = KVM_MAX_VCPUS;
 		break;

arch/s390/kvm/kvm-s390.c

···
 		else if (sclp.has_esca && sclp.has_64bscao)
 			r = KVM_S390_ESCA_CPU_SLOTS;
 		break;
-	case KVM_CAP_NR_MEMSLOTS:
-		r = KVM_USER_MEM_SLOTS;
-		break;
 	case KVM_CAP_S390_COW:
 		r = MACHINE_HAS_ESOP;
 		break;

arch/x86/kvm/x86.c

···
 	case KVM_CAP_MAX_VCPUS:
 		r = KVM_MAX_VCPUS;
 		break;
-	case KVM_CAP_NR_MEMSLOTS:
-		r = KVM_USER_MEM_SLOTS;
-		break;
 	case KVM_CAP_PV_MMU:	/* obsolete */
 		r = 0;
 		break;

virt/kvm/arm/arm.c

···
 	case KVM_CAP_MAX_VCPUS:
 		r = KVM_MAX_VCPUS;
 		break;
-	case KVM_CAP_NR_MEMSLOTS:
-		r = KVM_USER_MEM_SLOTS;
-		break;
 	case KVM_CAP_MSI_DEVID:
 		if (!kvm)
 			r = -EINVAL;

virt/kvm/kvm_main.c

···
 #endif
 	case KVM_CAP_MAX_VCPU_ID:
 		return KVM_MAX_VCPU_ID;
+	case KVM_CAP_NR_MEMSLOTS:
+		return KVM_USER_MEM_SLOTS;
 	default:
 		break;
 	}