pcm: route: Select slave chmap based on ttable information

pcm: route: Select slave chmap based on ttable information

It means we need to initialize this order:

 1) Read the ttable to figure out which channels are present
 2) Open slave pcm and find a matching chmap
 3) Determine size of ttable (this can now depend on the chmap)
 4) Read ttable coefficients
 5) At prepare time, select the matching chmap

Signed-off-by: David Henningsson <david.henningsson@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>