PM / Hibernate: Separate block_io

Move block I/O operations to a separate file. It is because it will
be used later not only by the swap writer.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

diff --cc kernel/power/Makefile
Simple merge

diff --cc kernel/power/block_io.c
Simple merge

diff --cc kernel/power/power.h
Simple merge

diff --cc kernel/power/swap.c
Simple merge