Sort headers alphabetically - it helps locating duplicates, and makes it
easier to figure out where to insert new headers. Alphabetic order should
also prove that each header is self-contained, i.e. can be included without
prerequisites.

Link: https://lore.kernel.org/r/20230202144628.14443-1-tudor.ambarus@linaro.orgSigned-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>