ARC: Move IOC enabling to compile-time options

Use CONFIG_ARC_DBG_IOC_ENABLE Kconfig option instead of
ioc_enable global variable.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
index e3f9db7..aee15d5 100644
--- a/arch/arc/Kconfig
+++ b/arch/arc/Kconfig
@@ -116,6 +116,24 @@
 	bool "Do not use Data Cache"
 	default n
 
+menuconfig ARC_DBG
+	bool "ARC debugging"
+	default n
+
+if ARC_DBG
+
+config ARC_DBG_IOC_ENABLE
+	bool "Enable IO coherency unit"
+	depends on CPU_ARCHS38
+	default n
+	help
+	  Enable IO coherency unit to debug problems with caches and
+	  DMA peripherals.
+	  NOTE: as of today linux will not work properly if this option
+	  is enabled in u-boot!
+
+endif
+
 choice
 	prompt "Target select"
 	default TARGET_AXS103