This changes apm.c to invoke suspend.c's save and restore processor
state procedures around suspends, which fixes the SYSENTER MSR problem.

The patch also decouples sysenter.c from SOFTWARE_SUSPEND: the variables
used (only!) in suspend_asm.S are moved there, and the include file now
declares the procedures called from apm.c (previously they were only
called from suspend_asm.S).