pinctrl: samsung: Remove old unused defines

Since 9a2c1c3b ("pinctrl: samsung: Allow grouping multiple
pinmux/pinconf nodes") the defines for GPIO group and function names are
not used anywhere in the driver.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Inspired-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>