vfio: replace CONFIG_HAVE_KVM with IS_ENABLED(CONFIG_KVM)

It is more accurate to Check if KVM is enabled, instead of having the
architecture say so. Architectures always "have" KVM, so for example
checking CONFIG_HAVE_KVM in vfio code is pointless, but if KVM is disabled
in a specific build, there is no need for support code.

Alternatively, the #ifdefs could simply be deleted. However, this
would add dead code. For example, when KVM is disabled, there is no
need to include code in VFIO that uses symbol_get, as that symbol_get
would always fail.

Cc: Alex Williamson <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Signed-off-by: Paolo Bonzini <[e-mail]>

drivers/vfio/vfio.h

···
 }
 #endif
 
-#ifdef CONFIG_HAVE_KVM
+#if IS_ENABLED(CONFIG_KVM)
 void vfio_device_get_kvm_safe(struct vfio_device *device, struct kvm *kvm);
 void vfio_device_put_kvm(struct vfio_device *device);
 #else

drivers/vfio/vfio_main.c

···
 #include <linux/fs.h>
 #include <linux/idr.h>
 #include <linux/iommu.h>
-#ifdef CONFIG_HAVE_KVM
+#if IS_ENABLED(CONFIG_KVM)
 #include <linux/kvm_host.h>
 #endif
 #include <linux/list.h>
···
 }
 EXPORT_SYMBOL_GPL(vfio_unregister_group_dev);
 
-#ifdef CONFIG_HAVE_KVM
+#if IS_ENABLED(CONFIG_KVM)
 void vfio_device_get_kvm_safe(struct vfio_device *device, struct kvm *kvm)
 {
 	void (*pfn)(struct kvm *kvm);