Add support for controlling mfi(4) controller properties:

allow user control of rebuild rate
allow user control of silence/enable alarm

MFC after:	2 weeks
Sponsored by:	Yahoo! Inc.
Extend loader_delay as-documented in beastie.4th(8) and delay.4th(8), making it available to architectures that do not use or load the beastie
menu. This is reported to save headaches on some PPC systems where unload
followed by load does not produce the desired results wherein if-given
the opportunicy to abort the initial loading sequence, you can customize
the first load.

Reviewed by:    nwhitehorn, kan
Discussed on:   -current