docs: build the Hafnium Hypervisor documentation

The Hafnium Hypervisor documentation is kept as a legacy provided this
component is still used for test purposes within the Hafnium CI.

As the original files are .md files as opposed to .rst files for the
remaining of the project, adjust tags to permit building with sphinx.

Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
Change-Id: I5fc138cf7bc2de1276823c0739cbca6d136f26dd
diff --git a/docs/hypervisor/FVP.md b/docs/hypervisor/FVP.md
index 8790bee..fde4016 100644
--- a/docs/hypervisor/FVP.md
+++ b/docs/hypervisor/FVP.md
@@ -22,7 +22,7 @@
 $ make && kokoro/test.sh --fvp
 ```
 
-See the `FvpDriver` class in [`hftest.py`](../test/hftest/hftest.py) for details
+See the `FvpDriver` class in [`hftest.py`](../../test/hftest/hftest.py) for details
 on how this works.
 
 ## Other resources