arc: minor fixes in Kconfig

 [1] Fix misspeling in ARC_CACHE_LINE_SHIFT dependency, now cache-line
lenth selection is correctly enabled if either I$ or D$ are enabled.

 [2] Add dummy entry to target list to make sure target type is always
mentioned in defconfig. Otherwise defconfig for the first target in the
list will not have target name and later on with addition of the new
target on top of the list in Kconfig will lead to corrupted
configuration expanded from defconfig.
Signed-off-by: NAlexey Brodkin <abrodkin@synopsys.com>

arch/arc/Kconfig

@@ -123,7 +123,7 @@ config ARC_CACHE_LINE_SHIFT
 	int "Cache Line Length (as power of 2)"
 	range 5 7
 	default "6"
-	depends on !SYS_DCACHE_OFF || !SYS_DCACHE_OFF
+	depends on !SYS_DCACHE_OFF || !SYS_ICACHE_OFF
 	help
 	  Starting with ARC700 4.9, Cache line length is configurable,
 	  This option specifies "N", with Line-len = 2 power N
@@ -133,6 +133,14 @@ config ARC_CACHE_LINE_SHIFT
 choice
 	prompt "Target select"
 
+config TARGET_DUMMY
+	bool "Dummy target"
+	help
+	  Please select one of real target boards below!
+	  This target is only meant to force "makedefconfig" to put
+	  TARGET_xxx in defconfig even this is the first target from the list
+	  below.
+
 config TARGET_TB100
 	bool "Support tb100"