NFC put the armv6m entry with the other Cortex-M entries

The armv6m entry in cores_match() got separated from its
friends armv7m and armv7em.  Reuniting them to make it
easier to keep them updated in all at the same time.

GitOrigin-RevId: 71a45e7c63285614364d3d5dfcb4d48da6e7535d
1 file changed