Use litevideo TMDS encoders

[gregdavill]

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It would be nice to remove the dependencies around the verilog DVI generation.

litevideo already includes a TMDS encoder module that should work in place of the verilog one. https://github.com/enjoy-digital/litevideo/blob/master/litevideo/output/hdmi/encoder.py

We would need to create a thin wrapper that handles the 10bit -> 2bit output using DDR modules at pix2x speed.

[gregdavill]

Some proof of concept code for this is in the develop branch.

https://github.com/gregdavill/DiVA-firmware/blob/develop/gateware/rtl/hdmi.py#L7-L31