Moving MIPS to Tier 2

[John Baldwin]

While reviewing the Tier document in the committers guide I noticed that mips
is currently listed as Tier 2.  However, I think it probably meets the
definition for Tier 2 (it not in external source code control for example)
and even some features of Tier 1 (cross-built packages are available).  One
note is that Tier 2 does require 3 active developers, but I think we probably
have that.  What do other folks think?

-- 
John Baldwin