dm: pmic: add s2mps11 PMIC I/O driver

dm: pmic: add s2mps11 PMIC I/O driver

This driver allows I/O operations on the Samsung S2MPS11 PMIC,
which provides lots of LDO/BUCK outputs.

To enable it, update defconfig with:
- CONFIG_PMIC_S2MPS11
and additional, if were not defined:
- CONFIG_CMD_PMIC
- CONFIG_ERRNO_STR

The binding info: doc/device-tree-bindings/pmic/s2mps11.txt

Signed-off-by: Przemyslaw Marczak <[email protected]>
Reviewed-by: Simon Glass <[email protected]>
Tested-by: Anand Moon <[email protected]>
Signed-off-by: Minkyu Kang <[email protected]>