dt-bindings: mtd: drop mtd/cortina,gemini-flash.txt

Drop mtd/cortina,gemini-flash.txt since it is nearly already handled by
Documentation/devicetree/bindings/mtd/mtd-physmap.yaml.

We add jedec-flash to list of compatible because one board (gemini-dlink-dns-313.dts) needs it.
See commit a10d862e ("ARM: dts: Fix the DNS-313 flash compatible")
The flash on the DNS-313 needs to be probed as JEDEC, it does not conform to the common CFI standard.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20220211120842.3388592-1-clabbe@baylibre.com