pinctrl: add function to parse generic pinconfig properties from a dt node

pinctrl: add function to parse generic pinconfig properties from a dt node

pinconf_generic_parse_dt_config() takes a node as input and generates an
array of generic pinconfig values from the properties of this node.

As I couldn't find a mechanism to count the number of properties of a node
the function uses internally an array to accept one of parameter and copies
the real present options to a smaller variable at its end.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
(cherry picked from commit 7db9af4b6e41be599e0fcd50d687138a5add428c)
Signed-off-by: Mark Brown <broonie@linaro.org>