pinctrl: uniphier: remove unneeded EXPORT_SYMBOL_GPL()

All UniPhier pinctrl drivers are built-in.  Exporting the symbol
is meaningless.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>