ARM: shmobile: r8a7740: Remove mapping of L2 cache controller registers

Now all r8a7740-based platforms have been migrated to the generic l2c OF
initialization, it's no longer needed to map the L2 cache controller
registers from .map_io().

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>