devtools: add checkpatch spelling dictionary builder

devtools: add checkpatch spelling dictionary builder

The script checkpatch.pl (used in checkpatches.sh) can use a dictionary
from the codespell project to check spelling.
There are multiple dictionaries to be used.

The script build-dict.sh concatenate multiple dictionaries and remove
some annoying false positives.

The dictionary built by this script must be saved in a file which
is referenced with the environment variable DPDK_CHECKPATCH_CODESPELL.
The easiest is to export this variable in ~/.config/dpdk/devel.config.

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>