MFC r310481:

Move the objects used to create temporary mappings for i386 pmap zero
and copy operations to the MD PCPU region. Change sysmap
initialization to only allocate KVA pages for CPUs that are actually
present. As a minor optimization, this also prevents false sharing
between adjacent sysmap objects since the pcpu struct is already
cacheline-aligned.

While here, move pc_qmap_addr initialization for the BSP into
pmap_bootstrap(), which allows use of pmap_quick* functions during
early boot.

Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D8833