drm/radeon/audio: fix missing multichannel PCM SAD in some cases

The current code writing SADs to the audio registers seems to assume
that there is at most a single SAD per audio format.

However, that is not the case. Especially for PCM it is somewhat common
for sinks to have two SADs, one for 8-channel and one for 2-channel
audio, which may have different supported sample rates (i.e. the sink
supports stereo audio at higher sample rates than multichannel audio).

Because of this, only the 2-channel SAD may be used if it appears before
the 8-channel SAD. Unless other SADs require otherwise, this may cause
the ALSA HDA driver to allow stereo playback only.

Fix the code to pick the PCM SAD with the highest number of channels,
while merging the rate masks of PCM SADs with lower amount of channels
into the additional stereo rate mask byte.

Technically there are even more cases to handle (multiple non-PCM SADs
of the same type, more than two PCM SADs with varying channel counts,
etc), but those have not actually been encountered in the field and
handling them would be non-trivial.

Example affected EDID from Onkyo TX-SR674 specifying 192kHz stereo
support and 96kHz 8-channel support (and other 8-channel compressed
formats):
00ffffffffffff003dcb010000000001
ffff0103800000780a0dc9a057479827
12484c00000001010101010101010101
010101010101011d8018711c1620582c
2500c48e2100009e011d007251d01e20
6e285500c48e2100001e000000fc0054
582d53523637342020202020000000fd
00313d0f2e08000a202020202020019b
02032f724f8504030f0e07069413121e
1d1615012f097f070f1f071707503707
503f07c0834f000066030c00ffff808c
0ad08a20e02d10103e9600c48e210000
18011d80d0721c1620102c2580c48e21
00009e011d00bc52d01e20b8285540c4
8e2100001e8c0ad090204031200c4055
00c48e210000180000000000000000a8

Signed-off-by: Anssi Hannula <anssi.hannula@iki.fi>
Tested-by: Andre Heider <a.heider@gmail.com>
Cc: Rafał Miłecki <zajec5@gmail.com>
Acked-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

diff --cc drivers/gpu/drm/radeon/dce6_afmt.c
Simple merge

diff --cc drivers/gpu/drm/radeon/evergreen_hdmi.c
Simple merge

diff --cc drivers/gpu/drm/radeon/r600_hdmi.c
Simple merge