scripts: add ABI checking utility

scripts: add ABI checking utility

There was a request for an abi validation utilty for the ongoing ABI stability
work.  As it turns out there is a abi compliance checker in development that
seems to be under active development and provides fairly detailed ABI compliance
reports.  Its not yet intellegent enough to understand symbol versioning, but it
does provide the ability to identify symbols which have changed between
releases, along with details of the change, and offers developers the
opportunity to identify which symbols then need versioning and validation for a
given update via manual testing.

This script automates the use of the compliance checker between two arbitrarily
specified tags within the dpdk tree.  To execute enter the $RTE_SDK directory
and run:

./scripts/validate_abi.sh $GIT_TAG1 $GIT_TAG2 $CONFIG

where $GIT_TAG1 and 2 are git tags and $CONFIG is a config specification
suitable for passing as the T= variable in the make config command.

Note the upstream source for the abi compliance checker is here:
http://ispras.linuxbase.org/index.php/ABI_compliance_checker

It generates a report for each DSO built from the requested tags that developers
can review to find ABI compliance issues.

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
Acked-by: Thomas Monjalon <thomas.monjalon@6wind.com>