power: supply: core: Use designated initializer for property text arrays

Use designated initializers for the sysfs power supply text values. This
will help ensure that the text values are kept in sync with the enum
values from power_supply.h.

Signed-off-by: Mathew King <mathewk@chromium.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>