Documentation: virtual: Add toctree hooks

Added toctree hooks for indexing. Hooks added only for newly added
files.

The hook for the top of the tree will be added in a later patch series
when a few more substantial changes have been added.
Signed-off-by: NLuke Nowakowski-Krijger <lnowakow@eng.ucsd.edu>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Documentation/virtual/index.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+============================
+Linux Virtualization Support
+============================
+
+.. toctree::
+   :maxdepth: 2
+
+   kvm/index
+   paravirt_ops
+
+.. only:: html and subproject
+
+   Indices
+   =======
+
+   * :ref:`genindex`

Documentation/virtual/kvm/index.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+===
+KVM
+===
+
+.. toctree::
+   :maxdepth: 2
+
+   amd-memory-encryption
+   cpuid