gpio: pxa: remove unused gpio_is_pxa_type function

clang with W=1 reports
drivers/gpio/gpio-pxa.c:174:19: error: unused function
  'gpio_is_pxa_type' [-Werror,-Wunused-function]
static inline int gpio_is_pxa_type(int type)
                  ^
This function is not used, so remove it.

Signed-off-by: Tom Rix <trix@redhat.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>