power: supply: core: allow to constify property lists

Since tables pointed to by power_supply_desc->properties and
->usb_types are not expected to change after registration, mark
the pointers accordingly

Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>