For some speakers and slots the CEA slot <-> speaker assignment depends
on the used CEA Channel Allocation value.

Therefore the from_cea_slot() and to_cea_slot() helpers currently only
work correctly for the regular 7.1 speakers.

Fix them to work with all speakers, taking the re-ordered CA index as
input and adapting use sites accordingly.

This change allows manual channel mapping to actually work for all CEA
allocated speakers. Additionally, this fixes incorrect channel map
reporting in automatic channel mapping mode when an affected speaker
position is used (e.g. 6.1 map which contains an RC speaker).
Signed-off-by: Anssi Hannula <anssi.hannula@iki.fi>
Signed-off-by: Takashi Iwai <tiwai@suse.de>