"Soft" Deconfigure Override

For any subsystem represented by a distinct device tree node, users may disable that function via the NVRAM variable asr-disable-list, which is simply a list of device tree paths separated by spaces.

ok setenv asr-disable-list /pci/ebus/ecpp /pci@1f,4000/scsi@3

The Ultra 450 OBP will use this information to created disabled status properties for each node listed in the variable asr-disable-list.