dm: regulator: add regulator command

This command is based on driver model regulator's API.
The user interface provides:
- list UCLASS regulator devices
- show or [set] operating regulator device
- print constraints info
- print operating status
- print/[set] voltage value [uV] (force)
- print/[set] current value [uA]
- print/[set] operating mode id
- enable the regulator output
- disable the regulator output

The 'force' option can be used for setting the value which exceeds
the constraints min/max limits.

Signed-off-by: Przemyslaw Marczak <p.marczak@samsung.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/common/Makefile b/common/Makefile
index 425658c..d6c1d48 100644
--- a/common/Makefile
+++ b/common/Makefile
@@ -214,6 +214,7 @@
 
 # Power
 obj-$(CONFIG_CMD_PMIC) += cmd_pmic.o
+obj-$(CONFIG_CMD_REGULATOR) += cmd_regulator.o
 endif
 
 ifdef CONFIG_SPL_BUILD