pinctrl: uniphier: support pin configuration in sparse pin space

Unfortunately, the pin number of the new SoC, PH1-LD11, is not
contiguous.  The base frame work must be adjusted to support the new
SoC pinctrl driver.  The pin_desc_get() exploits radix-tree for pin
look-up, so it works more efficiently with sparse pin space.

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