Remove Atmel AT91RM9200 and AT91SAM9 support.
The last known robust version of this code base was FreeBSD 8.2. There
are no users of this on current, and all users of it have abandoned
this platform or are in legacy mode with a prior version of FreeBSD.
All known users on arm@ approved this removal, and there were no
Differential Revision: https://reviews.freebsd.org/D16312