After 7470b80763, we refuse
to hibernate if we fail to write HibernateLocation EFI
variable and resume= is not set. Let's teach sleep_supported
to follow the practice too.
* "HibernateLocation" struct is renamed to HibernationDevice
to avoid ambiguity with the EFI variable. Also, it no longer
takes the reference to a SwapEntry object, since it's really
unnecessary (only SwapEntry.path is used), but increases complexity.
* SwapEntry is no longer used externally.
* find_hibernate_location is split into read_swap_entries and
find_suitable_hibernation_device. The former reads all swap entries
into SwapEntries object for later use.
* Make use of btrfs_get_file_physical_offset_fd
Closes#25130