Add internal tracking of smp startup status to reliably figure out
   what methods are to be used to get gtaskqueue up and running.

e1000:
   Calculating this pointer gives undefined behaviour when (last == -1)
   (it is before the buffer).  The pointer is always followed.  Panics
   occurred when it points to an unmapped page.  Otherwise, the pointed-to
   garbage tends to not have the E1000_TXD_STAT_DD bit set in it, so in the
   broken case the loop was usually null and the function just returned, and
   this was acidentally correct.

Submitted by:	bde
Reviewed by:	Matt Macy <mmacy@nextbsd.org>