net: ethernet: litex: Add the dependency on HAS_IOMEM

The LiteX driver uses devm io function API which
needs HAS_IOMEM enabled, so add the dependency on HAS_IOMEM.

Fixes: ee7da21a ("net: Add driver for LiteX's LiteETH network interface")
Signed-off-by: NCai Huoqing <cai.huoqing@linux.dev>
Link: https://lore.kernel.org/r/20220208013308.6563-1-cai.huoqing@linux.devSigned-off-by: NJakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/litex/Kconfig

@@ -17,7 +17,7 @@ if NET_VENDOR_LITEX
 
 config LITEX_LITEETH
 	tristate "LiteX Ethernet support"
-	depends on OF
+	depends on OF && HAS_IOMEM
 	help
 	  If you wish to compile a kernel for hardware with a LiteX LiteEth
 	  device then you should answer Y to this.