power: regulator: Add a driver for the AXP PMIC drivevbus

AXP PMICs have a pin which can either report the USB VBUS state, or
driving a regulator that supplies USB VBUS. Add a regulator driver for
controlling this pin. The selection between input and output is done via
the x-powers,drive-vbus-en pin on the PMIC (parent) node.

Signed-off-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Jernej Skrabec <jernej.skrabec@gmail.com>
diff --git a/drivers/power/pmic/axp.c b/drivers/power/pmic/axp.c
index 521a39d..c300fd2 100644
--- a/drivers/power/pmic/axp.c
+++ b/drivers/power/pmic/axp.c
@@ -51,6 +51,7 @@
 	{ "cldo",	"axp_regulator" },
 	{ "dc",		"axp_regulator" },
 	{ "dldo",	"axp_regulator" },
+	{ "drivevbus",	"axp_drivevbus" },
 	{ "eldo",	"axp_regulator" },
 	{ "fldo",	"axp_regulator" },
 	{ "ldo",	"axp_regulator" },