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_PCI_33_defconfig b/configs/sbc8548_PCI_33_defconfig
index 219700d..acb3092 100644
--- a/configs/sbc8548_PCI_33_defconfig
+++ b/configs/sbc8548_PCI_33_defconfig
@@ -14,6 +14,7 @@
 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_SYS_NS16550=y