gpio: xra1403: select REGMAP_SPI

Without the regmap code, we get a link error:

drivers/gpio/built-in.o: In function `xra1403_probe':
(.text+0x132e0): undefined reference to `__devm_regmap_init_spi'

Fixes: 5704520d ("gpio: xra1403: Add EXAR XRA1403 SPI GPIO expander driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Nandor Han <nandor.han@ge.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>