ARM: shmobile: sh73a0: Use ioremap() to map L2C registers

Replace using the legacy IOMEM() macro to map the L2C registers by
ioremap().

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20201117103022.2136527-6-geert+renesas@glider.be