keymap: Unite laptop models needing common volume-key release quirk

Many laptop models need the same volume-key release quirk. Currently, two
models have identical force-release-maps/ keymap files (dell-studio-1557 and
fujitsu-amilo-si1848) and two more need to be added (Mitac and Coolbox QBook).

This replaces the identical force-release-maps files with one
'common-volume-keys' file to make adding new models easier.

There is no obvious DMI commonality between the models needing the quirk (i.e.
they do not all share the same BIOS), so it will remain necessary to scan for
each model separately in 95-keyboard-force-release.rules.

https://launchpad.net/bugs/565459

Signed-off-by: Martin Pitt <martin.pitt@ubuntu.com>