alsactl: Add a --with-udev-rules-dir configure option.

alsactl: Add a --with-udev-rules-dir configure option.

After the previous patch to install udev rules it is impossible to do a
non-root, custom-prefix make install. This is generally not a problem
when building official packages but it can be a pain for developers
and debuggers etc.

This is essentially the same patch as was already made in PulseAudio
in commit e8a5746f2fcae59bfd18d39b621509b3ef130453.

Signed-off-by: Colin Guthrie <gmane@colin.guthr.ie>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>