PM / hibernate: Add CONFIG_HIBERNATION_IMAGE_REUSE

By default this hibernation image is erased after either a successful or
unsuccessful hibernation restore sequeunce. Since filesystem contents on
disk are not part of the hibernation image, failure to create a new
hibernation image every boot can lead to filesystem corruption.

Conversely, if the usecase can guarantee that the filesystem is not ever
modified, the same hibernation image can be reused. This prevents
creating additional hibernation images unncesarily.

For more details, refer to the description of CONFIG_HIBERNATION for
booting without resuming.

Change-Id: I4a8d5aba170bbf00f837804c2df26d8d8d682af2
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>