power: pmic: sunxi: add AXP313 SPL driver

On boards using the AXP313 PMIC, the DRAM rail is often not setup
correctly at reset time, so we have to program the PMIC very early in
the SPL, before running the DRAM initialisation.

Add a simple AXP313 PMIC driver that knows about DCDC2(CPU) and
DCDC3(DRAM), so that we can bump up the voltage before the DRAM init.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Jernej Skrabec <jernej.skrabec@gmail.com>
diff --git a/arch/arm/mach-sunxi/pmic_bus.c b/arch/arm/mach-sunxi/pmic_bus.c
index c090840..8e7625f 100644
--- a/arch/arm/mach-sunxi/pmic_bus.c
+++ b/arch/arm/mach-sunxi/pmic_bus.c
@@ -22,6 +22,7 @@
 #define AXP209_I2C_ADDR			0x34
 
 #define AXP305_I2C_ADDR			0x36
+#define AXP313_I2C_ADDR			0x36
 
 #define AXP221_CHIP_ADDR		0x68
 
@@ -34,6 +35,8 @@
 		return AXP152_I2C_ADDR;
 	if (IS_ENABLED(CONFIG_AXP305_POWER))
 		return AXP305_I2C_ADDR;
+	if (IS_ENABLED(CONFIG_AXP313_POWER))
+		return AXP313_I2C_ADDR;
 
 	/* Other AXP2xx and AXP8xx variants */
 	return AXP209_I2C_ADDR;