Convert CONFIG_CMD_IO to Kconfig

This converts the following to Kconfig:
   CONFIG_CMD_IO

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/Kconfig b/arch/Kconfig
index ed6b6a0..a8a13b7 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -69,6 +69,7 @@
 	select DM_GPIO
 	select DM_MMC
 	imply CMD_HASH
+	imply CMD_IO
 
 config SH
 	bool "SuperH architecture"
@@ -89,6 +90,7 @@
 	select DM_MMC if MMC
 	imply CMD_FPGA_LOADMK
 	imply CMD_GETTIME
+	imply CMD_IO
 
 config XTENSA
 	bool "Xtensa architecture"