Port r212559 to mips.
Port r212559 to mips.

Do not explicitly enable interrupts in smp_init_secondary() because it
renders any spinlock protected code after that point to run with
interrupts enabled. This is because the processor is executing in the
context of idlethread whose 'md_spinlock_count' is already set to 1.

Instead just let sched_throw() re-enable interrupts when it releases
the spinlock.

The original powerpc commit log for r212559 is available here:
http://svn.freebsd.org/viewvc/base?view=revision&revision=212559

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase