Update LCD display instructions

[JamesH65]

Needed updating for the FKMS change on Pi4.

[6by9]

Looks reasonable.
I could insert the rotate=X line into the command line if it was viewed useful. Seeing as X ignores it, I'm not sure it is.

[lurch]

Just noticed that this page (outside of the text being edited in this PR) mentions both display_lcd_rotate and display_hdmi_rotate - is one of them wrong?

[lurch]

Does the FKMS mode support the "flip" option that the Legacy mode supports?

[lurch]

"The DSI display is designed to work with Raspberry Pi models 2, 3 and 4 that have mounting holes in a HAT footprint. Model 1 A/B boards are supported, but require additional mounting hardware to fit the HAT-dimensioned stand-offs on the display PCB."

Minor nitpick - which category do the Model 1 A+ and B+ fall into?

[6by9]

Does the FKMS mode support the "flip" option that the Legacy mode supports?

Yes, you can add reflect_x and reflect_y as well as rotate=N to the video= entry in cmdline.txt

[JamesH65]

Does the FKMS mode support the "flip" option that the Legacy mode supports?

Yes, you can add reflect_x and reflect_y as well as rotate=N to the video= entry in cmdline.txt

Does this need to be added to the PR?

[JamesH65]

Unless people want the reflect items added, I'm inclined to merge this. Any objections or improvements?

[ghost]

"The DSI display is designed to work with Raspberry Pi models 2, 3 and 4 that have mounting holes in a HAT footprint. Model 1 A/B boards are supported, but require additional mounting hardware to fit the HAT-dimensioned stand-offs on the display PCB."

Minor nitpick - which category do the Model 1 A+ and B+ fall into?

The Pi 1 model A+ and B+ are the same shape as the later boards, and have the mounting holes in the same place. Perhaps this sentence should instead read:

"The DSI display is designed to work on all models of Raspberry Pi, however early models (The Raspberry Pi 1 model A and B) will require additional mounting hardware to fit the HAT-dimensioned stand-offs on the display PCB."

[JamesH65]

Have made a change similar to that suggested by @andrum99 , any other comment prior to merging?