mfd: AXP20x: Add mfd driver for AXP20x PMIC

This patch introduces the preliminary support for PMICs X-Powers AXP202
and AXP209. The AXP209 and AXP202 are the PMUs (Power Management Unit)
used by A10, A13 and A20 SoCs and developed by X-Powers, a sister company
of Allwinner.

The core enables support for two subsystems:
- PEK (Power Enable Key)
- Regulators

Signed-off-by: Carlo Caione <carlo@caione.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
index e166d71..c681741 100644
--- a/drivers/mfd/Kconfig
+++ b/drivers/mfd/Kconfig
@@ -67,6 +67,18 @@
 	help
 	  Support for the BCM590xx PMUs from Broadcom
 
+config MFD_AXP20X
+	bool "X-Powers AXP20X"
+	select MFD_CORE
+	select REGMAP_I2C
+	select REGMAP_IRQ
+	depends on I2C=y
+	help
+	  If you say Y here you get support for the X-Powers AXP202 and AXP209.
+	  This driver include only the core APIs. You have to select individual
+	  components like regulators or the PEK (Power Enable Key) under the
+	  corresponding menus.
+
 config MFD_CROS_EC
 	tristate "ChromeOS Embedded Controller"
 	select MFD_CORE