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------------ /sys/devices/virtual/amhdmitx/amhdmitx0/rawedid ------------
0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
^ That from the CE dump confirms that there is bad (zero) EDID data on the HDMI connection. The difference between the vendor kernel and mainline is that the vendor kernel includes a bunch of forced defaults which allow things to work. The upstream kernel doesn't, so there is no active video or audio connection. If you've tried other cables and TVs then I'd guess something got damaged in the HDMI socket.
The one thing you can try is configuring the box to use an edid.bin file, and substitute the edid.bin captured from another device.