doc: Update HIPC documentation with Open vSwitch and VLAN

Update the documentation about HIPC introducing the Open vSwitch
and VLAN concept and how the network topology is affected by the
introduction.

Add an entry in the dictionary for the checker and a reference to
the Open vSwitch website in Sphinx configuration file.

Signed-off-by: Luca Fancellu <luca.fancellu@arm.com>