buildroot

mysql: Make S97mysqld source a default file

Hardcoded parameters are used for mysql user/directory.

Make S97mysqld source a /etc/default/mysql file where these
parameters can be overridden.

Signed-off-by: Eloi BAIL <eloi.bail@savoirfairelinux.com>
Tested-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>