This adds a custom swap file service, which allows specifying a
recommended swap size in the deviceinfo file via
`deviceinfo_swap_size_recommended`. For the N900 this defaults
to 1024 MB now. As the swap file is created in the root partition,
we have encrypted swap now (unless encryption is disabled with
`--no-fde`).
This is a workaround for #429, until the iteration count can be
specified directly in cryptsetup.
* Add default iter-time option, and option to override
* set SHA1 default hash for luksFormat, add option to override
* [RX51] load omap-sham in initramfs for HW accel. sha1
