MFC r284683:

MFC r284683:
 Enable ttyu1, ttyu2, ttyu3 for arm installations.

 This should make all consoles available, whether it
 is VGA, HDMI, serial, or JTAG, but more importantly
 enables all consoles when ttyu0 is not predictable.
 For example, the Pandaboard ES apparently has three
 consoles available, but the DB9/RS232 serial port is
 ttyu2, so not available by default after the system
 boots.

Sponsored by:	The FreeBSD Foundation

git-svn-id: svn://svn.freebsd.org/base/stable/10@284775 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f