dt-bindings: vendor-prefixes: Document Argon40

Argon 40 Technologies Limited is a SBC expansion board vendor.
Document the prefix. For details see https://argon40.com

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Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Link: https://lore.kernel.org/r/20250629220757.936212-1-marek.vasut+renesas@mailbox.org


Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>