configs: Restore SND_PCM_OSS=m

A kconfig change way back in 4.13 caused SND_PCM_OSS to be dropped from
our defconfigs. Restore it as a potential workaround for a supposed
bug.

See: https://github.com/raspberrypi/linux/issues/3883



Signed-off-by: Phil Elwell <phil@raspberrypi.com>