ARM: shmobile: r8a7779: Use ioremap() to map SMP registers

Replace using the legacy IOMEM() macro to map the ARM Reset Vector
Address Register (AVECR) by ioremap().

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20201117103022.2136527-4-geert+renesas@glider.be