Use dev/apm/files.apm for APM options in opt_apm.h.

Now both apm and apmdev files.apm can be included so you can switch
from apmdev0 to apm0 at hpcapm0 in your kernel config easily.

Rework hpcapm(4) attachment definition so it is not required to attach at
mainbus, and convert its two users, hpcsh and hpcmips, to that.

Many thanks to Valeriy Ushakov and Ben Collver for testing.

merge ktrace-lwp.

hpcmips independent part are moved to sys/dev/hpc/