re: kern/45361: Consistent kernel panic when building qemu in amd64

[matthew green <mrg%eterna.com.au@localhost>]

this change includes this diff:

-       emergva = uvm_km_alloc(kernel_map, round_page(MAXPHYS), 0,
+       emergva = uvm_km_alloc(kernel_map,
+           round_page(MAXPHYS) + ptoa(uvmexp.ncolors), 0,

however, there's no accounting for if uvm_page_recolor() is ever called
like it is on x86, ppc and sparc64, so later if using this space we're
going to trash on someone else's memory.


.mrg.