conf: load function (hook) - add OR support

conf: load function (hook) - add OR support

While I was trying to work on XDG_CONFIG_HOME support, I though
that it may be nice to support OR for the file specification.

But then I found that we can already do this via the refer hook.

I commit this change anyway, because the snd_config_hook_load()
function is more clean now.

The OR is implemented with three | characters like:

  "~/.asoundrc|||~/.asoundrc2|||/opt/some/other/path"

(first file found wins)

Signed-off-by: Jaroslav Kysela <perex@perex.cz>