Documentation: move Documentation/virtual to Documentation/virt

Renaming docs seems to be en vogue at the moment, so fix on of the
grossly misnamed directories.  We usually never use "virtual" as
a shortcut for virtualization in the kernel, but always virt,
as seen in the virt/ top-level directory.  Fix up the documentation
to match that.

Fixes: ed16648eb5 ("Move kvm, uml, and lguest subdirectories under a common "virtual" directory, I.E:")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/powerpc/include/uapi/asm/kvm_para.h

@@ -31,7 +31,7 @@
  * Struct fields are always 32 or 64 bit aligned, depending on them being 32
  * or 64 bit wide respectively.
  *
- * See Documentation/virtual/kvm/ppc-pv.txt
+ * See Documentation/virt/kvm/ppc-pv.txt
  */
 struct kvm_vcpu_arch_shared {
 	__u64 scratch1;