ARM: shmobile: r8a7740: Migrate to generic l2c OF initialization

Migrate the generic r8a7740 platform from calling l2x0_of_init() to the
generic l2c OF initialization.

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