ALSA: docs: Extend module parameters description

ALSA: docs: Extend module parameters description

Common ALSA module parameters look a little bit confusing because of the
description lacking, and it took me a while to understand the purpose of
their existence. To figure it out I asked the question about them to the
"alsa-devel" mailing list, and Takashi Iwai answered me with the text I
appended to the ALSA documentation in this patch.

These common module parameters aren't used a lot nowadays, but as I
understand they are important for providing compatibility with some
existing user-space apps. So in my opinion it is a good idea to document
why we need them.

Signed-off-by: Ivan Orlov <ivan.orlov0322@gmail.com>
Link: https://lore.kernel.org/r/20230501101634.476297-1-ivan.orlov0322@gmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>