bsd-user: Add scheduler and cpuset functions to os-misc.h

Expand os-misc.h with scheduler functions (sched_setparam,
sched_getparam, sched_setscheduler, sched_getscheduler,
sched_rr_get_interval) and CPU affinity functions (cpuset,
cpuset_setid, cpuset_getid, cpuset_getaffinity, cpuset_setaffinity).
Also add sched_yield, sched_get_priority_min, and
sched_get_priority_max to bsd-proc.h.

Signed-off-by: Stacey Son <sson@FreeBSD.org>
Signed-off-by: Sean Bruno <sbruno@FreeBSD.org>
Signed-off-by: Mikaël Urankar <mikael.urankar@gmail.com>
Assisted-by: Claude Opus 4.6 (1M context)
Acked-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Warner Losh <imp@bsdimp.com>