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/sbc8548_defconfig b/configs/sbc8548_defconfig
index b239a86..185825e 100644
--- a/configs/sbc8548_defconfig
+++ b/configs/sbc8548_defconfig
@@ -13,6 +13,7 @@
 CONFIG_CMD_MII=y
 CONFIG_CMD_PING=y
 # CONFIG_CMD_HASH is not set
+# CONFIG_CMD_IRQ is not set
 # CONFIG_MMC is not set
 CONFIG_MTD_NOR_FLASH=y
 # CONFIG_PCI is not set