dt-bindings: gpio-mmio: Correct opencores GPIO

In commit f48b5e8bc2e1 ("dt-bindings: gpio-mmio: Add compatible string
for opencores,gpio") we marked opencores,gpio to be allowed with
brcm,bcm6345-gpio. This was wrong, opencores,gpio is not compatible with
brcm,bcm6345-gpio. It has a different register map and is 8-bit vs
Broadcom which is 32-bit. Change opencores,gpio to be a separate
compatible string for MMIO GPIO.

Also, as this change rewrote the entire enum, I took this opportunity to
alphabetically sort the list.

Fixes: f48b5e8bc2e1 ("dt-bindings: gpio-mmio: Add compatible string for opencores,gpio")
Signed-off-by: Stafford Horne <shorne@gmail.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20260115151014.3956805-2-shorne@gmail.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>