userspace: improve dynamic object allocation

We now have a low-level function z_dynamic_object_create()
which is not a system call and is used for installing
kernel objects that are not supported by k_object_alloc().

Checking for valid object type enumeration values moved
completely to the implementation function.

A few debug messages and comments were improved.

Futexes and sys_mutexes are now properly excluded from
dynamic generation.

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>