Create a separate structure for per-CPU state saved across suspend and
resume that is a superset of a pcb. Move the FPU state out of the pcb and
into this new structure. As part of this, move the FPU resume code on
amd64 into a C function. This allows resumectx() to still operate only on
a pcb and more closely mirrors the i386 code.

Reviewed by: kib (earlier version)