Incorrect references to A1/A2 cards only being from sandisk

[theofficialgman]

At the time of this writing A1 and A2 cards are only widely available from SanDisk. Armbian recommends A1 rated SD-Cards only now ([A2 rated cards need yet lacking driver support and therefore show lower overall and especially random IO performance](https://github.com/ThomasKaiser/Knowledge/blob/master/articles/A1_and_A2_rated_SD_cards.md)). For example:

this is all simply incorrect.

For a better explanation and better card recommendations refer to here https://wiki.switchroot.org/wiki/sd-card-guide

[EvilOlaf]

This part has been written several years ago and not refactored since then.
Feel free to contribute and provide a PR to fix this.