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>