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/Kconfig b/drivers/power/Kconfig
index f8f0239..d03626e 100644
--- a/drivers/power/Kconfig
+++ b/drivers/power/Kconfig
@@ -1,3 +1,7 @@
+menu "Power"
+
+source "drivers/power/pmic/Kconfig"
+
 config AXP221_POWER
 	boolean "axp221 / axp223 pmic support"
 	depends on MACH_SUN6I || MACH_SUN8I
@@ -73,3 +77,5 @@
 	disable eldo3. On some A31(s) tablets it might be used to supply
 	1.2V for the SSD2828 chip (converter of parallel LCD interface
 	into MIPI DSI).
+
+endmenu