power/supply: Drop obsolete JZ4740 driver

It has been replaced with the more mature ingenic-battery driver.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Tested-by: Artur Rojek <contact@artur-rojek.eu>
Acked-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Paul Burton <paul.burton@mips.com>