Overlay for GalaxyCore GC9A01 displays

[juliannojungle]

This includes an overlay for easy use of displays based on GalaxyCore's GC9A01 single chip driver, attaching them on spi0 as fb1 framebuffer.

Originally created at https://github.com/juliannojungle/gc9a01-overlay where includes all documentation. Merging in raspberrypi kernel for easy use of said displays on future Raspberry Pi OS releases.

[pelwell]

Hi @juliannojungle,

I'm not familiar with the GC9A01 display, but the overlay looks like it could work - I'm sure you've been using it enough that we can say it has been tested. I have a few problems with the Pull Request:

1. I guess you used the GitHub editor to add the overlay source - it uses DOS line endings (each line has a carriage return (0xd/Ctrl-M) as well as a line feed (0xa/Ctrl-J)). This looks ugly using the Git tools.
2. The "✨" is attention-seeking.
3. We require a README entry for each overlay - see https://github.com/raspberrypi/linux/blob/rpi-5.15.y/arch/arm/boot/dts/overlays/README. You should be able to copy most of it from a similar overlay such as piscreen. Please preserve the alphabetical ordering, strict indentation (spaces only - no TABs), and two blank lines between entries.
4. You'll also need to add an entry to the Makefile (https://github.com/raspberrypi/linux/blob/rpi-5.15.y/arch/arm/boot/dts/overlays/Makefile). Again, respect the alphabetical ordering.

[juliannojungle]

Hi, @pelwell!
Yes, I've been using this overlay for quite some time. It works nicely on the display I have.
The "2 - ✨" thing is a commit message pattern adopted by many repositories, based on some rules. The "sparkles" means "introducing new feature". I tottaly missed that I shouldn't be using that here, sorry for that. Already removed.
I'll fix the first topic (carriage return and line feed) and adjust the files from topics 3 and 4 later today.

Thank you very much for the instructions about the merge (I searched the wiki but couldn't find any guidelines).

[juliannojungle]

Hi, @pelwell. I believe I fixed said problems with the Pull Request now. Thank you for taking time to instruct me on how to proceed.

[pelwell]

Nice job. I forgot to mention the compatible string - I prefer to use just brcm,bcm2835 for overlays compatible with all Pis and brcm,bcm2711 for those that only work with Pi 4 - so I've pushed a fix-up patch.