kvm: Make VM ioctl do valloc for some archs

The kvm struct has been bloating. For example, it's tens of kilo-bytes
for x86, which turns out to be a large amount of memory to allocate
contiguously via kzalloc. Thus, this patch does the following:
1. Uses architecture-specific routines to allocate the kvm struct via
   vzalloc for x86.
2. Switches arm to __KVM_HAVE_ARCH_VM_ALLOC so that it can use vzalloc
   when has_vhe() is true.

Other architectures continue to default to kalloc, as they have a
dependency on kalloc or have a small-enough struct kvm.

Signed-off-by: Marc Orr <marcorr@google.com>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

virt/kvm/arm/arm.c

@@ -251,6 +251,21 @@ long kvm_arch_dev_ioctl(struct file *filp,
 	return -EINVAL;
 }
 
+struct kvm *kvm_arch_alloc_vm(void)
+{
+	if (!has_vhe())
+		return kzalloc(sizeof(struct kvm), GFP_KERNEL);
+
+	return vzalloc(sizeof(struct kvm));
+}
+
+void kvm_arch_free_vm(struct kvm *kvm)
+{
+	if (!has_vhe())
+		kfree(kvm);
+	else
+		vfree(kvm);
+}
 
 struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm, unsigned int id)
 {