Convert CONFIG_CMD_IRQ to Kconfig

This converts the following to Kconfig:
   CONFIG_CMD_IRQ

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/io_defconfig b/configs/io_defconfig
index 27edc59..d1b5a03 100644
--- a/configs/io_defconfig
+++ b/configs/io_defconfig
@@ -21,6 +21,7 @@
 # CONFIG_CMD_NFS is not set
 CONFIG_CMD_MII=y
 CONFIG_CMD_PING=y
+# CONFIG_CMD_IRQ is not set
 # CONFIG_MMC is not set
 CONFIG_MTD_NOR_FLASH=y
 # CONFIG_PCI is not set