pinctrl: bcm2835: Add support for generic pinctrl binding

To keep driver up to date we add generic pinctrl binding support, which
covers the features used in this driver and has additional node properties
that this SoC has compatibility, so enabling future implementations of
these properties without the need to create new node properties in the
device trees.

The logic of this change maintain the old brcm legacy binding support in
order to keep the ABI stable.

Signed-off-by: Matheus Castello <matheus@castello.eng.br>
Reviewed-by: Eric Anholt <eric@anholt.net>
Acked-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>