pinctrl: palmas: add pincontrol driver

TI Palmas series Power Management IC have multiple pins which can be
configured for different functionality. This pins can be configured
for different function. Also their properties like pull up/down,
open drain enable/disable are configurable.

Add support for pincontrol driver Palmas series device like TPS65913,
TPS80036. The driver supports to be register from DT only.

Changes from V1:
- Add generic property for pins and functions in pinconf-generic.
- Add APIs to map the DT and subnode.
- Move common utils APIs to the pinctrl-utils from this file.
- Update the binding document accordingly.
Changes from V2:
- Add ack by Lee.
- Correct the binding docs.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>