module loader dead code removal and cleanups v3

Hi all,

this series removes support for long term unused export types and
cleans up various loose ends in the module loader.

Changes since v2:
 - clean up klp_find_object_symbol a bit
 - remove the now unused module_assert_mutex helper 

Changes since v1:
 - move struct symsearch to module.c
 - rework drm to not call find_module at all
 - allow RCU-sched locking for find_module
 - keep find_module as a public API instead of module_loaded
 - update a few comments and commit logs

Diffstat: