Optimize for R10k CPUs in machines like the SGI O2

Contact: port-mips

NetBSD/sgimips currently runs on O2s with R10k (or similar) CPUs, but for example speculative loads are not handled correctly. It is unclear if this is pure kernel work or the toolchain needs to be changed too.

Currently softfloat is used, and bugs seem to exist in the hardware float support. Resolving these bugs and switching to hardware float would improve performance.