mk: add a paused deprecation warning before each build

mk: add a paused deprecation warning before each build

DPDK 20.05 had some deprecation notes after "make config"
and after the build.
For DPDK 20.08, the config note is replaced with a warning
before the config and before the build.
After the warning, there is a pause which can be skipped
with the variable MAKE_PAUSE.

This deprecation process was discussed in the Technical Board:
http://mails.dpdk.org/archives/dev/2020-April/162839.html

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