page color initialization

[Masao Uebayashi <uebayasi%gmail.com@localhost>]

The current code seems to allow to change uvmexp.ncolors at
configure() -> cpu_attach() -> uvm_page_recolor().  I think changing
uvmexp.ncolors after uvm_init() is too late, and allocating such
fundamental data like page freelist buckets that late is best to
avoid.

How about:

- determine cache size in MD boot code, by querying the primary CPU
(supposing that this should not need lots of infrastructure like
dynamic memory allocation / bus interaction)

- determine uvmexp.ncolors before calling init_main()/uvm_init()/uvm_page_init()

- if configure() finds a CPU whose cache size doesn't match the
primary CPU, just reject to attach it

?

Masao