Connor Abbott wrote a nice explanation of how instance divisors work on Mali.
Let's add it to the driver docs instead of letting it languish in a forgotten
header file.
This is mostly pasted from the existing header in tree, with a few local changes
applied.
Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20445>