drm/amd/display: update soc bb for nv14

drm/amd/display: update soc bb for nv14

[ Upstream commit d5349775c1726ce997b8eb4982cd85a01f1c8b42 ]

[why]
nv14 previously inherited soc bb from generic dcn 2, did not match
watermark values according to memory team

[how]
add nv14 specific soc bb: copy nv2 generic that it was
using from before, but changed num channels to 8

Signed-off-by: Martin Leung <martin.leung@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>