hdspmixer: Save and restore level meter settings

hdspmixer: Save and restore level meter settings

Each preset can have a different level meter setting (FS samples for
OVR, release rate, minimum level and so on).

These settings were not saved/restore to/from the on-disk file. This
patch adds the missing functionality.

Unfortunately, the current on-disk format is a 1:1 binary dump from
memory without any header information. In other words, this commit will
break backward compatibility with older hdspmixers, that is, new preset
files cannot be read by older versions of hdspmixer. However, we can
still read the old mix files and save them in the new format.

I hence bumped the version, so users know to re-create their files after
upgrading to 1.11.

Bug discovered by Raphaël Doursenaud from ematech.fr.

Signed-off-by: Adrian Knoth <adi@drcomp.erfurt.thur.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>