PM / hibernate: Make passing hibernate offsets more friendly

Currently the only way to specify a hibernate offset for a
swap file is on the kernel command line.

Add a new /sys/power/resume_offset that lets userspace
specify the offset and disk to use when initiating a hibernate
cycle.

Change-Id: Ied0be8062e6677e44acbfcb8cbf235e6bb8cf2ef
Signed-off-by: Mario Limonciello <mario.limonciello@dell.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Git-commit: 355064675f1c997cea017ea64c8f2c216e5425d9
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Yimin Peng <yiminp@codeaurora.org>