doc: render and install man pages

This enables the rendering of rst into man pages as well as installing
them (if built) along the binaries. To do so there is a new make target
"doc-guides-man" which will render the rst files into man format.

Currently these three tools had docs that were compatible "enough" to
make up for a reasonable manpage.
- testpmd
- dpdk-pdump
- dpdk-procinfo

Since a man page should be installed along the binary they are not
installed in install-doc but install-runtime insteade. If not explicitly
built by the "doc-guides-man" target before calling install-runtime
there is no change to the old behaviour.

Signed-off-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>
Acked-by: Luca Boccassi <lboccass@brocade.com>
Acked-by: John McNamara <john.mcnamara@intel.com>