mtd: nand: ecc: mxic: Fix compile test issue

Avoid random build errors with architectures which do not select
HAS_IOMEM by depending on it in Kconfig.

This fixes the following warning:

/home/mraynal/0day/gcc-11.2.0-nolibc/s390-linux/bin/s390-linux-ld:
drivers/mtd/nand/ecc-mxic.o: in function `mxic_ecc_probe':
ecc-mxic.c:(.text+0x2244): undefined reference to `devm_platform_ioremap_resource'

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20220314152336.75447-1-miquel.raynal@bootlin.com