Remove syscalls that allows user threads to set callbacks that
will be invoked by the kernel.
Userspace is not trusted we can't allow a user thread set callbacks
that will be invoked by the kernel and run with supervisor privileges.
Signed-off-by: Flavio Ceolin <flavio.ceolin@intel.com>
Move the syscall_handler.h header, used internally only to a dedicated
internal folder that should not be used outside of Zephyr.
Signed-off-by: Anas Nashif <anas.nashif@intel.com>
The callbacks API was similar to gpio / espi callbacks API. Refactor
it to use more intuitive names for set / remove callbacks.
Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@intel.com>
