infra/common: Update virtualization documentation

Pull out the I/O virtualization related documetation to a separate page
to accommodate for future additions. Also update the Virtualization
documentation to align with the updated software stack.

Signed-off-by: Vivek Gautam <vivek.gautam@arm.com>
Change-Id: Ib29e678a32fa8360918b1536e133e2da7c58ac86