doc: update build instructions in the Linux guide

doc: update build instructions in the Linux guide

Before removing the "make" build system completely,
the Linux guide instructions are made more concise and accurate.
Some detailed explanations are also available in
doc/guides/prog_guide/dev_kit_root_make_help.rst

This is the swan song for makefile system,
in order to have accurate information backported in LTS.

Cc: stable@dpdk.org
Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: David Marchand <david.marchand@redhat.com>