Add CONFIG_DEBUG_SG sg validation

Add a Kconfig entry which will toggle some sanity checks on the sg
entry and tables.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index c567f21..1faa508 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -389,6 +389,16 @@
 
 	  If unsure, say N.
 
+config DEBUG_SG
+	bool "Debug SG table operations"
+	depends on DEBUG_KERNEL
+	help
+	  Enable this to turn on checks on scatter-gather tables. This can
+	  help find problems with drivers that do not properly initialize
+	  their sg tables.
+
+	  If unsure, say N.
+
 config FRAME_POINTER
 	bool "Compile the kernel with frame pointers"
 	depends on DEBUG_KERNEL && (X86 || CRIS || M68K || M68KNOMMU || FRV || UML || S390 || AVR32 || SUPERH || BFIN)