async_tx: remove HIGHMEM64G restriction

This restriction prevented ASYNC_TX_DMA from being enabled on platform
configurations where DMA address conversion could not be performed in
place on the stack.  Since commit 04ce9ab ("async_xor: permit callers
to pass in a 'dma/page scribble' region") the async_tx api now either
uses a caller provided 'scribble' buffer, or performs the conversion in
place when sizeof(dma_addr_t) <= sizeof(struct page *).

Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/dma/Kconfig

@@ -128,7 +128,7 @@ config NET_DMA
 
 config ASYNC_TX_DMA
 	bool "Async_tx: Offload support for the async_tx api"
-	depends on DMA_ENGINE && !HIGHMEM64G
+	depends on DMA_ENGINE
 	help
 	  This allows the async_tx api to take advantage of offload engines for
 	  memcpy, memset, xor, and raid6 p+q operations.  If your platform has