use default target (but not for host) device settings on
ahc(4) interface without its SEEPROM (mostly on-board one).
This flag could be useful if host's BIOS (firmware) initializes
ahc(4) chip with some conservative (async, no tagged queuing etc.)
target settings for minimum support to load its primary loader etc.,
and it will be enabled in each attachment according to MD device
properties(9). Currently this property is set only on sgimips for
O2 on-board aic7880 adapters.
No objection on tech-kern (and netbsd-bugs), and closes PR kern/23276.