power: supply: "usb_type" property may be written to

According to Documentation/ABI/testing/sysfs-class-power the "usb_type"
property is Read-Only.

For power-supplies which consume USB power such as battery charger chips,
this is correct.

But the UCS1002 USB Port Power Controller driver which is a driver
for a chip which is a power-source for USB-A charging ports "usb_type"
is actually writable to configure the type of USB charger emulated
by the USB-A port.

Adjust the docs and the power_supply_sysfs.c code to adjust for this
new writeable use of "usb_type":

1. Update Documentation/ABI/testing/sysfs-class-power to document that
"usb_type" may be writable

2. Change the power_supply_attr type in power_supply_sysfs.c from
POWER_SUPPLY_ATTR() into POWER_SUPPLY_ENUM_ATTR() so that the various
usb_type string values from POWER_SUPPLY_TYPE_TEXT[] such as e.g.
"SDP" and "USB_PD" can be written to the "usb_type" attribute instead
of only accepting integer values.

Cc: Enric Balletbo Serra <enric.balletbo@collabora.com>
Cc: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20240831142039.28830-2-hdegoede@redhat.comSigned-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

Documentation/ABI/testing/sysfs-class-power

@@ -592,7 +592,12 @@ Description:
 		the supply, for example it can show if USB-PD capable source
 		is attached.
 
-		Access: Read-Only
+		Access: For power-supplies which consume USB power such
+		as battery charger chips, this indicates the type of
+		the connected USB power source and is Read-Only.
+
+		For power-supplies which act as a USB power-source such as
+		e.g. the UCS1002 USB Port Power Controller this is writable.
 
 		Valid values:
 			      "Unknown", "SDP", "DCP", "CDP", "ACA", "C", "PD",

drivers/power/supply/power_supply_sysfs.c

@@ -209,7 +209,7 @@ static struct power_supply_attr power_supply_attrs[] = {
 	POWER_SUPPLY_ATTR(TIME_TO_FULL_NOW),
 	POWER_SUPPLY_ATTR(TIME_TO_FULL_AVG),
 	POWER_SUPPLY_ENUM_ATTR(TYPE),
-	POWER_SUPPLY_ATTR(USB_TYPE),
+	POWER_SUPPLY_ENUM_ATTR(USB_TYPE),
 	POWER_SUPPLY_ENUM_ATTR(SCOPE),
 	POWER_SUPPLY_ATTR(PRECHARGE_CURRENT),
 	POWER_SUPPLY_ATTR(CHARGE_TERM_CURRENT),