mkinitfs: add support for resume

Created by: stwa

This patch tries to add resume from hibernation (aka suspend to disk) support to mkinitfs. The swap partition can be provided via the resume option.

I know this feature is mostly needed on destops/notebooks, therefore I'm not sure if there is any interest for Alpine Linux. The default Alpine Linux kernel has no hibernation support compiled in, so you need to build a custom kernel in order to test this.

These links helped me on the topic:

• https://wiki.gentoo.org/wiki/Custom_Initramfs/Hibernation
• https://git.archlinux.org/mkinitcpio.git/tree/hooks/resume

As this might be a dangerous feature I would like to get your opinions.