ARM: s3c24xx: fix Wunused-variable warning on !MMU

If S3C24xx machine code is build without CONFIG_MMU, the iotable()
macros do nothing so annotate structures to get rid of warnings:

  arch/arm/mach-s3c24xx/common.c:140:24: warning: ‘s3c_iodesc’ defined but not used [-Wunused-variable]
  arch/arm/mach-s3c24xx/s3c2410.c:49:24: warning: ‘s3c2410_iodesc’ defined but not used [-Wunused-variable]
  arch/arm/mach-s3c24xx/s3c2412.c:60:24: warning: ‘s3c2412_iodesc’ defined but not used [-Wunused-variable]
  arch/arm/mach-s3c24xx/s3c2416.c:54:24: warning: ‘s3c2416_iodesc’ defined but not used [-Wunused-variable]
  arch/arm/mach-s3c24xx/s3c2443.c:45:24: warning: ‘s3c2443_iodesc’ defined but not used [-Wunused-variable]
  arch/arm/mach-s3c24xx/s3c244x.c:44:24: warning: ‘s3c244x_iodesc’ defined but not used [-Wunused-variable]

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200910154150.3318-2-krzk@kernel.org