infra/utils: add helper to generate comma-separated lists

infra/utils: add helper to generate comma-separated lists

Add a helper macro that, from a space-separated list of items, returns a
comma-separated list of the quoted items.

This will be useful when we need to generate lists in JSON, later...

Code suggested by Thomas P.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas De Schampheleire <patrickdepinguin@gmail.com>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: Arnout Vandecappelle <arnout@mind.be>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>