docs/sphinx: Fix FUSA indexing

Sphinx complains:

  docs/fusa/index.rst:6: WARNING: toctree contains reference to nonexisting document 'fusa/reqs'
  docs/fusa/reqs/index.rst:6: WARNING: toctree contains reference to nonexisting document 'fusa/reqs/market-reqs'
  docs/fusa/reqs/index.rst:6: WARNING: toctree contains reference to nonexisting document 'fusa/reqs/product-reqs'
  docs/fusa/reqs/index.rst:6: WARNING: toctree contains reference to nonexisting document 'fusa/reqs/design-reqs/arm64'

  docs/fusa/index.rst: WARNING: document isn't included in any toctree
  docs/fusa/reqs/design-reqs/arm64/generic-timer.rst: WARNING: document isn't included in any toctree
  docs/fusa/reqs/design-reqs/arm64/sbsa-uart.rst: WARNING: document isn't included in any toctree
  docs/fusa/reqs/index.rst: WARNING: document isn't included in any toctree
  docs/fusa/reqs/market-reqs/reqs.rst: WARNING: document isn't included in any toctree
  docs/fusa/reqs/product-reqs/arm64/reqs.rst: WARNING: document isn't included in any toctree

Fix the toctrees.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Ayan Kumar Halder <ayan.kumar.halder@amd.com>

docs/fusa/index.rst

@@ -6,4 +6,4 @@ Functional Safety documentation
 .. toctree::
    :maxdepth: 2
 
-   reqs
+   reqs/index

docs/fusa/reqs/index.rst

@@ -7,6 +7,7 @@ Requirements documentation
    :maxdepth: 2
 
    intro
-   market-reqs
-   product-reqs
-   design-reqs/arm64
+   market-reqs/reqs
+   product-reqs/arm64/reqs
+   design-reqs/arm64/generic-timer
+   design-reqs/arm64/sbsa-uart

docs/index.rst

@@ -65,6 +65,7 @@ Documents in need of some rearranging.
    designs/launch/hyperlaunch-devicetree
    misc/xen-makefiles/makefiles
    misra/index
+   fusa/index
 
 
 Miscellanea