monit: bump to version 3.12.2

Also add hash file and remove the m4 directory creation from the monit.mk
which is now in the source tree.

[Thomas: as suggested by Baruch, keep only upstream sha256 hash.]

Signed-off-by: Sebastien Bourdelin <sebastien.bourdelin@savoirfairelinux.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>