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>

arch/unicore32/mm/Kconfig

@@ -43,7 +43,4 @@ config CPU_TLB_SINGLE_ENTRY_DISABLE
 config SWIOTLB
 	def_bool y
 	select DMA_DIRECT_OPS
-
-config NEED_SG_DMA_LENGTH
-	def_bool SWIOTLB
-
+	select NEED_SG_DMA_LENGTH