gpio: mmio: Add compatible for opencores GPIO

On FPGA Development boards with GPIOs the OpenRISC architecture uses the
opencores gpio verilog rtl.  This is compatible with the gpio-mmio.  Add
the compatible string to allow probing this driver from the devicetree.

Link: https://opencores.org/projects/gpio
Signed-off-by: Stafford Horne <shorne@gmail.com>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20260115151014.3956805-3-shorne@gmail.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>

Author: stffrdhrn

drivers/gpio/gpio-mmio.c

@@ -724,6 +724,7 @@ static const struct of_device_id gpio_mmio_of_match[] = {
 	{ .compatible = "wd,mbl-gpio" },
 	{ .compatible = "ni,169445-nand-gpio" },
 	{ .compatible = "intel,ixp4xx-expansion-bus-mmio-gpio" },
+	{ .compatible = "opencores,gpio" },
 	{ }
 };
 MODULE_DEVICE_TABLE(of, gpio_mmio_of_match);