EDAC: Boundary-check edac_debug_level

Only levels [0:4] are allowed so enforce that. Also, while at it,
massage Kconfig text and add valid debug levels range to the module
parameter description.

Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
diff --git a/drivers/edac/Kconfig b/drivers/edac/Kconfig
index 409b92b..bb82d6b 100644
--- a/drivers/edac/Kconfig
+++ b/drivers/edac/Kconfig
@@ -42,10 +42,10 @@
 config EDAC_DEBUG
 	bool "Debugging"
 	help
-	  This turns on debugging information for the entire EDAC
-	  sub-system. You can insert module with "debug_level=x", current
-	  there're four debug levels (x=0,1,2,3 from low to high).
-	  Usually you should select 'N'.
+	  This turns on debugging information for the entire EDAC subsystem.
+	  You do so by inserting edac_module with "edac_debug_level=x." Valid
+	  levels are 0-4 (from low to high) and by default it is set to 2.
+	  Usually you should select 'N' here.
 
 config EDAC_DECODE_MCE
 	tristate "Decode MCEs in human-readable form (only on AMD for now)"