MFC: r267321

Avoid the USB device disconnected and controller shutdown clutter on system
shutdown by putting the former under !rebooting and turning the latter into
debug messages.

Reviewed by:	hps
Sponsored by:	Bally Wulff Games & Entertainment GmbH
MFC: r267638

Don't denounce peripherals on system shutdown. Together with r267321
(MFCed to stable/10 in r267775), we're now back to the pre-r228483
level of default verbosity. This in turn again typically allows for
reading information that userland might have printed on the screen
before initiating a halt, but still permits to debug potential device
shutdown problems on system shutdown via CAM_DEBUG etc.

Reviewed by:	mav
Sponsored by:	Bally Wulff Games & Entertainment GmbH