new-bus: Use M_WAITOK in more places

[jhb]

Summary

M_NOWAIT is now only used for devclass_get_devices,
devclass_get_drivers, and device_get_children. Other functions are
generally called from sleepable contexts such as module event
handlers, attach/detach routines, and the ioctl handler for
/dev/devctl2.

Suggested by: mjg (devclass_add_device)

[jhb]

This booted fine for me (no WITNESS warnings) in both a bhyve VM and my X1 Carbon.

sys/kern/subr_bus.c

2119

This didn't really handle failure

[imp]

I think i chamged some of these in my tree. Now if i could jusr find that