LWP private support / TLS support

[Joerg Sonnenberger <joerg%britannica.bec.de@localhost>]

Hi all,
I've just committed the first major step to TLS support on NetBSD.
The ARM part is very rudimentary. It only covers the equivalent of
the lwp_setprivate/lwp_getprivate system calls. It doesn't provide a
fast access path yet. I am not aware of a CPU register that can be used
for this purpose, so a CPU specific page mapping for userland is needed
to properly support SMP. It would be great if someone with ARM
experience could pick this up and provide the necessary changes for the
pmap. Feel free to contact me for questions of how this should be
exposed to userland and integrated with the rest.

Joerg