ARM: nspire: Remove unneeded nspire_map_io()

nspire_map_io() just calls debug_ll_io_init().

If machine_desc.map_io is not set, devicemaps_init() in the
common ARM code will call debug_ll_io_init(), so nspire_map_io() and the
initialization of .map_io can be removed.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Vladimir Murzin <vladimir.murzin@arm.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>