MFC r255117:
Fix the build with CTLFEDEBUG, broken by unmapped I/O support changes.
MFC 249028:

The CTL block backend is broken without this.

  Fix sending virtual scatter/gather lists from the CTL CAM frontend
  peripheral.

  Sponsored by:	Spectra Logic

(cherry picked from commit e7d4fe3d7770f5799b70e023d020c45cd6505817)