Initial DP alt mode support

Clearly not ready to be merged since the tps65982x is full of debugging and it enforces host mode but having this in an MR makes it a bit easier to track. Further todos are runtime PM, automatic enablement of power output (which is where !205 (closed) should help) and support for pre dogwood hw (which also needs !205 (closed)).

(all the other bits are coming in via https://source.puri.sm/guido.gunther/linux-imx8/-/tree/mrs/5.9/display-stack which @martin.kepplinger already merge in so this is 5.9+ only)

Closes: #223 (closed) , OS-issues#97 (closed)