Some SoCs are either supposed to be pin compatible (A10 and A20 for
example), or are just repackaged versions of the same die (A10s, A13, GR8).

In those case, having a full blown pinctrl driver just introduces
duplication in both data size and maintainance effort.

Add a variant option to both pins and functions to be able to limit the
pins and functions described only to a subset of the SoC we support with a
given driver.
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>