gpio: qixis: select CONFIG_REGMAP_MMIO

gpio: qixis: select CONFIG_REGMAP_MMIO

The regmap drivers need to be selected by each user, without that there
can be configurations that fail to link:

x86_64-linux-ld: drivers/gpio/gpio-qixis-fpga.o: in function `qixis_cpld_gpio_probe':
gpio-qixis-fpga.c:(.text+0x13a): undefined reference to `__devm_regmap_init_mmio_clk'

Fixes: e88500247dc3 ("gpio: add QIXIS FPGA GPIO controller")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20251204094928.1031494-1-arnd@kernel.org
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>