nvmem: rmem: fix undefined reference to memremap

Fix below error reporte by kernel test robot
rmem.c:(.text+0x14e): undefined reference to memremap
s390x-linux-gnu-ld: rmem.c:(.text+0x1b6): undefined reference to memunmap

Fixes: 5a3fa75a ("nvmem: Add driver to expose reserved memory as nvmem")
Reported-by: kernel test robot <lkp@intel.com>
Reviewed-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20210330111241.19401-9-srinivas.kandagatla@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/nvmem/Kconfig

@@ -272,6 +272,7 @@ config SPRD_EFUSE
 
 config NVMEM_RMEM
 	tristate "Reserved Memory Based Driver Support"
+	depends on HAS_IOMEM
 	help
 	  This driver maps reserved memory into an nvmem device. It might be
 	  useful to expose information left by firmware in memory.