pinctrl: uniphier: omit redundant input enable bit information

For LD11/20 SoCs (capable of per-pin input enable), the iectrl bit
number matches its pin number.  So, this is redundant information.
Instead, we just need a flag to know if the iectrl gating exists or not.

With this refactoring, 5 bits in pin data will be saved.

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