arcmsr(4): Sync with FreeBSD (1.20.00.25 -> 1.20.00.29).

Adds support for ARC1214, ARC1224, ARC1264, ARC1284, and ARC1883, mainly.

Unfortunately, lots of style fixes, whitespace adjustment, etc. are mixed up
in it too, so it's a rather large commit.

Also, this upgrade has so far only been tested with my ARC-1210.