pinctrl: abx500: Staticize some symbols

These symbols are used only in this file. Without this patch
we get the following warnings:
drivers/pinctrl/pinctrl-abx500.c:520:5: warning:
symbol 'abx500_gpio_request' was not declared. Should it be static?
drivers/pinctrl/pinctrl-abx500.c:527:6: warning:
symbol 'abx500_gpio_free' was not declared. Should it be static?
drivers/pinctrl/pinctrl-abx500.c:614:5: warning:
symbol 'abx500_gpio_request_enable' was not declared. Should it be static?
drivers/pinctrl/pinctrl-abx500.c:714:5: warning:
symbol 'abx500_pin_config_get' was not declared. Should it be static?
drivers/pinctrl/pinctrl-abx500.c:721:5: warning:
symbol 'abx500_pin_config_set' was not declared. Should it be static?

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Acked-by: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>