userspace: add additional debug to elf_helper

Devices are identified as belonging to a particular subsystem
by looking at device->driver_api.

Print some debug information if this is NULL or points to an
unrecognized API struct.

This is normal in a lot of cases, for example any use of SYS_INIT().
However, for real devices this may be an indication of mis-
configuration.

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