add support for DSI as an internal display option

There is good reason to suspect the lack of DSI identification is causing the failure of rotation on Pine devices (according to qtmir, the display is registering as Unknown-2 - but mirserver is saying Output 2 on DSI, meaning it should call it DSI-2, not Unknown-2). in mir's graphics/display_configuration.h, this is already identified correctly. The only place where the DSI matching does not line up is mir's include/miral/miral/output.h - if this patch fails, then that is the missing dependency.

UPDATE: While these changes haven't worked yet, I have tested a build of qtmir that turns https://gitlab.com/ubports/development/core/qtmir/-/blob/main/src/platforms/mirserver/platformscreen.cpp?ref_type=heads#L179 this "if" off, making the sensor on by default. Sure enough, the PinePhone Pro is now rotating beautifully. But we still need a correct fix, which should detect that this is internal.

UPDATE 2: It works now!

To get everything working all in one for rotation on Pine64 devices, we need the following (these are not blocking this merge):

1. this merge (!69 (merged))
2. DeviceInfo update (deviceinfo!23 (merged))
3. Greeter fix (lomiri!109 (merged))
4. Optional: miral enumeration (ubports/development/core/packaging/mir!9 (merged))
5. WIP: external display ordering fix (lomiri!111 (closed))