gpio: pca953x: Add regmap dependency for PCA953x driver

Select REGMAP_I2C in Kconfig, since the driver now depends on regmap
and this was missing, thus breaking build on various systems.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>