Debian Busters is the new stable so let's upgrade.

v2: stay on stretch for MIPS

Cc: Guillaume Tucker <guillaume.tucker@collabora.com>
Cc: Petri Latvala <petri.latvala@intel.com>
Issue: https://bugs.debian.org/932725


Signed-off-by: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
Reviewed-by: Petri Latvala <petri.latvala@intel.com>