Documentation: KVM: add separate directories for architecture-specific documentation

ARM already has an arm/ subdirectory, but s390 and x86 do not even though
they have a relatively large number of files specific to them.  Create
new directories in Documentation/virt/kvm for these two architectures
as well.

While at it, group the API documentation and the developer documentation
in the table of contents.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20220322110712.222449-2-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Documentation/virt/kvm/index.rst

@@ -8,25 +8,13 @@ KVM
    :maxdepth: 2
 
    api
-   amd-memory-encryption
-   cpuid
-   halt-polling
-   hypercalls
-   locking
-   mmu
-   msr
-   nested-vmx
-   ppc-pv
-   s390-diag
-   s390-pv
-   s390-pv-boot
-   timekeeping
-   vcpu-requests
-
-   review-checklist
+   devices/index
 
    arm/index
+   s390/index
+   ppc-pv
+   x86/index
 
-   devices/index
-
-   running-nested-guests
+   locking
+   vcpu-requests
+   review-checklist

Documentation/virt/kvm/s390/index.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+====================
+KVM for s390 systems
+====================
+
+.. toctree::
+   :maxdepth: 2
+
+   s390-diag
+   s390-pv
+   s390-pv-boot

Documentation/virt/kvm/x86/index.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+===================
+KVM for x86 systems
+===================
+
+.. toctree::
+   :maxdepth: 2
+
+   amd-memory-encryption
+   cpuid
+   halt-polling
+   hypercalls
+   mmu
+   msr
+   nested-vmx
+   running-nested-guests
+   timekeeping