mtd: rawnand: add unspecified HAS_IOMEM dependency

Currently CONFIG_MTD_NAND_CADENCE implicitly depends on
CONFIG_HAS_IOMEM=y; consequently, on architectures without IOMEM we get
the following build error:

ld: drivers/mtd/nand/raw/cadence-nand-controller.o: in function `cadence_nand_dt_probe.cold.31':
drivers/mtd/nand/raw/cadence-nand-controller.c:2969: undefined reference to `devm_platform_ioremap_resource'
ld: drivers/mtd/nand/raw/cadence-nand-controller.c:2977: undefined reference to `devm_ioremap_resource'

Fix the build error by adding the unspecified dependency.

Reported-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>