dm: pmic: add implementation of driver model pmic uclass

This commit introduces the PMIC uclass implementation.
It allows providing the basic I/O interface for PMIC devices.
For the multi-function PMIC devices, this can be used as I/O
parent device, for each IC's interface. Then, each PMIC particular
function can be provided by the child device's operations, and the
child devices will use its parent for read/write by the common API.

Core files:
- 'include/power/pmic.h'
- 'drivers/power/pmic/pmic-uclass.c'

The old pmic framework is still kept and is independent.

For more detailed informations, please look into the header file.

Changes:
- new uclass-id: UCLASS_PMIC
- new config: CONFIG_DM_PMIC

Signed-off-by: Przemyslaw Marczak <p.marczak@samsung.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/power/pmic/Kconfig b/drivers/power/pmic/Kconfig
new file mode 100644
index 0000000..d06d632
--- /dev/null
+++ b/drivers/power/pmic/Kconfig
@@ -0,0 +1,11 @@
+config DM_PMIC
+	bool "Enable Driver Model for PMIC drivers (UCLASS_PMIC)"
+	depends on DM
+	---help---
+	This config enables the driver-model PMIC support.
+	UCLASS_PMIC - designed to provide an I/O interface for PMIC devices.
+	For the multi-function PMIC devices, this can be used as parent I/O
+	device for each IC's interface. Then, each children uses its parent
+	for read/write. For detailed description, please refer to the files:
+	- 'drivers/power/pmic/pmic-uclass.c'
+	- 'include/power/pmic.h'