soc: mediatek: mmsys: Specify HAS_IOMEM dependency for MTK_MMSYS

Because mtk-mmsys uses the 'devm_platform_ioremap_resource' function, it
should depend on HAS_IOMEM.

Fixes: cc657602 ("soc: mediatek: mmsys: Use devm_platform_ioremap_resource()")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>
Link: https://lore.kernel.org/r/20201203121447.3366406-1-enric.balletbo@collabora.com


Signed-off-by: Arnd Bergmann <arnd@arndb.de>