power: pmic: sunxi: use generic AXP SPL driver for AXP313

The generic AXP SPL driver implementation can cover all regulators we
need for the AXP313.

Add the descriptions for the three DC/DC regulators of the AXP313, and
enable that when CONFIG_AXP313_POWER is enabled. Also remove the old
driver, and switch the Makefile to include the new, generic version.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
diff --git a/drivers/power/Makefile b/drivers/power/Makefile
index 67161b3..312edec 100644
--- a/drivers/power/Makefile
+++ b/drivers/power/Makefile
@@ -13,7 +13,7 @@
 obj-$(CONFIG_AXP152_POWER)	+= axp152.o
 obj-$(CONFIG_AXP209_POWER)	+= axp209.o
 obj-$(CONFIG_AXP305_POWER)	+= axp305.o
-obj-$(CONFIG_AXP313_POWER)	+= axp313.o
+obj-$(CONFIG_AXP313_POWER)	+= axp_spl.o
 obj-$(CONFIG_AXP717_POWER)	+= axp_spl.o
 obj-$(CONFIG_AXP809_POWER)	+= axp809.o
 obj-$(CONFIG_AXP818_POWER)	+= axp818.o