drm/amd/display: set Layout properly for 8ch audio at timing validation

Why:
For audio packet type 0x02, there are 2 Layouts:
   Layout = 0 for 2 channels
and Layout = 1 for > 2 channels.
Layout will affect bandwidth check.

Currently, for HDMI FRL, Layout field isn't set and has a default value
of 0, so theoretically only 2-channel audio for audio packet type 0x02
is supported now.

How:
1. Set Layout properly according to maximum audio channel numbers for
audios with audio packet type 0x02.
2. 8ch LPCM audio is not supported for timing modes with v_active <= 576.

Reviewed-by: Chris Park <chris.park@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Acked-by: Agustin Gutierrez <agustin.gutierrez@amd.com>
Signed-off-by: Bing Guo <Bing.Guo@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>