ARM: mm: kill unused runtime hook arch_iounmap()

Since the following commits,

v5.4
  commit 59d3ae9a ("ARM: remove Intel iop33x and iop13xx support")
v5.11
  commit 3e3f354b ("ARM: remove ebsa110 platform")

The runtime hook arch_iounmap() on ARM is useless, kill arch_iounmap()
and __iounmap().

Cc: Russell King <linux@armlinux.org.uk>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/r/20220607125027.44946-2-wangkefeng.wang@huawei.com


Signed-off-by: Will Deacon <will@kernel.org>