Collapse gd_astpending and gd_reqpri together into gd_reqflags. gd_reqflags

Collapse gd_astpending and gd_reqpri together into gd_reqflags.  gd_reqflags
now rollsup requests made pending for doreti.  Cleanup a number of scheduling
primitives and note that we do not need to use locked bus cycles on per-cpu
variables.

Note that the aweful idelayed hack for certain softints (used only by the TTY
subsystem, BTW) gets slightly broken in this commit because idelayed has become
per-cpu and the clock ints aren't yet distributed.