mtd: gpmi: document current clock requirements

The clock requirements are completely missing, add the clocks
currently required by the driver.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
1 file changed