scatterlist: move the NEED_SG_DMA_LENGTH config symbol to lib/Kconfig

This way we have one central definition of it, and user can select it as
needed.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
diff --git a/lib/Kconfig b/lib/Kconfig
index 2f69085..aeb7fae 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -429,6 +429,9 @@
 	bool
 	default n
 
+config NEED_SG_DMA_LENGTH
+	bool
+
 config IOMMU_HELPER
 	bool