John Baldwin f418f79ce2 Revert the IPI startup sequence to match what is described in the
Intel Multiprocessor Specification v1.4.  The Intel SDM claims that
the INIT IPIs here are invalid, but other systems follow the MP
spec instead.

While here, fix the IPI wait routine to accept a timeout in microseconds
instead of a raw spin count, and don't spin forever during AP startup.
Instead, panic if a STARTUP IPI is not delivered after 20 us.

PR:		196542
Differential Revision:	https://reviews.freebsd.org/D1719
MFC after:	2 weeks
2015-02-06 18:19:59 +00:00
..
2015-01-01 18:43:31 +00:00