Support for 16KB pages sizes committed.

[Matt Thomas <jabbathespud%gmail.com@localhost>]

To avoid an issue with caching on the Gdium I added support for 16KB  
pages on MIPS for non-MIPS1 CPUs.  To enable it add this to your  
config file:

options         ENABLE_MIPS_16KB_PAGE
no options      VMSWAP_UAREA

and let me know how it works.  Your system should have lots of RAM  
since you will have 75% less pages.

One side effect of the options above is that all lwp's user areas  
(stacks) are now direct mapped and avoid the TLB.  This should  
slightly improve performance in addition to reduced TLB refills due to  
the larger the page size.  This always means if your L1 caches no  
longer have virtual aliases at 16KB (which is true for the Loongson2  
in the GDIUM) all your pages will remain cached all the time.