pinctrl: add utility functions for add map/configs

Some of pincontrol driver needs the utility function to create map
list. The utility function needed for adding mux, configs etc.

In place of duplicating this in each driver, add the common utility
function in common file and use from device specific driver. This will
reduce the duplicating of code across drivers.

Changes from V1:
- Add this files in this patch and add common utility APIs to here.

Changes from V2:
- Nothing in code.
- Added Reviewed by Stephen.

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