ARM: at91: add pinctrl support

This is also include the gpio controller as the IP share both.
Each soc will have to describe the SoC limitation and pin configuration via
DT.

This will allow to do not need to touch the C code when adding new SoC if the
IP version is supported.

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>