x86: Save registers in saved_context during suspend and hibernation

During hibernation and suspend on x86_64 save CPU registers in the saved_context
structure rather than in a handful of separate variables.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>