[S390] hibernation: fix guest page hinting related crash

On resume the system that loads the to be resumed image might have
unstable pages.
When the resume image is copied back and a write access happen to an
unstable page this causes an exception and the system crashes.

To fix this set all free pages to stable before copying the resumed
image data. Also after everything has been restored set all free
pages of the resumed system to unstable again.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>