Changes

vty: fix osmo_cpu_sched_vty_init() prototype

Change return type of osmo_cpu_sched_vty_init() from void to int
to match its implementation.

This fixes a prototype mismatch rejected by stricter compilers
(e.g. Emscripten).

Change-Id: Ia86e8063178ad82de098c2ff693cfbcd7e9f2192

vty: make CPU scheduling optional based on platform support

Add configure checks for sched_* APIs and guard their usage
in cpu_sched_vty with HAVE_SCHED_* macros.

If scheduler functions are not available, return -ENOTSUP
instead of failing at build time.

This improves portability on platforms lacking full sched
support (e.g. non-Linux or restricted environments).

Change-Id: Ic5b7e39fac16531d370cb81f769ba87fef18cb81