The repository obeys an 100 character soft limit for source lines.
However, commit messages generally have lines shorter than 72 characters
to make gerrit print them without wrapping.

Annoyingly, the editorconfig can't express this and the 100 character
limit applies to commit messages, requiring manual formatting. Luckily,
when writing commit messages the file `.git/COMMIT_EDITMSG` is open. So
we can set its line length to be 72 characters.

Change-Id: Id96dcab8ce500ee965e53dd53a51c6761811440e
Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>