power: regulator: Add a driver for AXP PMIC regulators

This driver handles most voltage regulators found in X-Powers AXP PMICs.
It is based on, and intended to replace, the regulator driver in TF-A.

AXP PMIC regulators can be divided into 6 categories:
 - Switches without voltage control => fully supported.
 - Single linear range => fully supported.
 - Two linear ranges, "step" and "2 * step" => fully supported.
 - Two linear ranges, "step" and "5 * step" => only the first range is
   supported. No boards are known to use the second range.
 - Non-linear voltage values => fully supported.
 - LDOs shared with GPIO pins => not supported.

Signed-off-by: Samuel Holland <samuel@sholland.org>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
diff --git a/drivers/power/regulator/Kconfig b/drivers/power/regulator/Kconfig
index c02e637..c346d03 100644
--- a/drivers/power/regulator/Kconfig
+++ b/drivers/power/regulator/Kconfig
@@ -43,6 +43,20 @@
 	  but does not yet support change voltages. Currently this must be
 	  done using direct register writes to the PMIC.
 
+config REGULATOR_AXP
+	bool "Enable driver for X-Powers AXP PMIC regulators"
+	depends on DM_REGULATOR && PMIC_AXP
+	help
+	  Enable support for the regulators (DCDCs, LDOs) in the
+	  X-Powers AXP152, AXP2xx, and AXP8xx PMICs.
+
+config SPL_REGULATOR_AXP
+	bool "Enable driver for X-Powers AXP PMIC regulators in SPL"
+	depends on SPL_DM_REGULATOR && SPL_PMIC_AXP
+	help
+	  Enable support in SPL for the regulators (DCDCs, LDOs) in the
+	  X-Powers AXP152, AXP2xx, and AXP8xx PMICs.
+
 config DM_REGULATOR_BD71837
 	bool "Enable Driver Model for ROHM BD71837/BD71847 regulators"
 	depends on DM_REGULATOR && DM_PMIC_BD71837