This moves the subsystem->ctrlrs list management fully into the
subsystem code, which will help simplify thread safety considerations
once we start adding locks.
Change-Id: Ibc118923f1bd520f1e524cde5d45ccfcc69aee1e
Signed-off-by: Daniel Verkamp <daniel.verkamp@intel.com>
Reviewed-on: https://review.gerrithub.io/376025
Tested-by: SPDK Automated Test System <sys_sgsw@intel.com>