Add SMP/i386 suspend/resume support.
Most part is merged from amd64.

• i386/acpica/acpi_wakecode.S

Replaced with amd64 code (from realmode to paging enabling code).

• i386/acpica/acpi_wakeup.c

Replaced with amd64 code (except for wakeup_pagetables stuff).

• i386/include/pcb.h
• i386/i386/genassym.c

Added PCB new members (CR0, CR2, CR4, DS, ED, FS, SS, GDT, IDT, LDT
and TR) needed for suspend/resume, not for context switch.

• i386/i386/swtch.s

Added suspendctx() and resumectx().
Note that savectx() was not changed and used for suspending (while
amd64 code uses it).
BSP and AP execute the same sequence, suspendctx(), acpi_wakecode()
and resumectx() for suspend/resume (in case of UP system also).

• i386/i386/apic_vector.s

Added cpususpend().

• i386/i386/mp_machdep.c
• i386/include/smp.h

Added cpususpend_handler().

• i386/include/apicvar.h
• kern/subr_smp.c
• sys/smp.h

Added IPI_SUSPEND and suspend_cpus().

• i386/i386/initcpu.c
• i386/i386/machdep.c
• i386/include/md_var.h
• pc98/pc98/machdep.c

Moved initializecpu() declarations to md_var.h.

MFC after: 3 days