ARM: sunxi: Remove the .map_io function declaration

debug_ll_io_init should be enough to map the needed addresses at boot,
so remove the trivial map_io code, and let the core call
debug_ll_io_init.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>