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/arch/powerpc/cpu/mpc83xx/Kconfig b/arch/powerpc/cpu/mpc83xx/Kconfig
index 02e43bc..0772b7c 100644
--- a/arch/powerpc/cpu/mpc83xx/Kconfig
+++ b/arch/powerpc/cpu/mpc83xx/Kconfig
@@ -49,6 +49,7 @@
 
 config TARGET_MPC8349ITX
 	bool "Support MPC8349ITX"
+	imply CMD_IRQ
 
 config TARGET_MPC837XEMDS
 	bool "Support MPC837XEMDS"