ARM: shmobile: sh73a0: Remove obsolete static mapping

There are no more users of the statically mapped IOMEM region on
SH-Mobile AG5.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20201117103022.2136527-8-geert+renesas@glider.be