devtools: add IWYU script to remove unused includes

devtools: add IWYU script to remove unused includes

This script can be used for removing headers flagged for removal by the
include-what-you-use (IWYU) tool. The script has the ability to remove
headers from specified sub-directories or dpdk as a whole and tests the
build after each removal by calling meson compile.

example usages:

Remove headers flagged by iwyu_tool output file
$ ./devtools/process_iwyu.py iwyu.out -b build

Remove headers flagged by iwyu_tool output file from sub-directory
$ ./devtools/process_iwyu.py iwyu.out -b build -d lib/kvargs

Remove headers directly piped from the iwyu_tool
$ iwyu_tool -p build | ./devtools/process_iwyu.py - -b build

Signed-off-by: Sean Morrissey <sean.morrissey@intel.com>
Signed-off-by: Conor Fogarty <conor.fogarty@intel.com>
Reviewed-by: Bruce Richardson <bruce.richardson@intel.com>