memory: omap-gpmc: Use a compatible match table when checking for NAND controller

As more compatibles can be added to the GPMC NAND controller driver
use a compatible match table.

Signed-off-by: Roger Quadros <rogerq@kernel.org>
Acked-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/r/20211221131757.2030-4-rogerq@kernel.org


[krzysztof: remove "is_nand" variable]
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>