MIPS: IP27: Switch from DMA_IP27 to DMA_COHERENT

The special IP27 DMA code selected by DMA_IP27 has been removed a while
ago turning DMA_IP27 into almost a nop.  Also fixup the broken logic of
its last users memcpy.S and memcpy-inatomic.s.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/lib/memcpy.S b/arch/mips/lib/memcpy.S
index c06cccf..56a1f85 100644
--- a/arch/mips/lib/memcpy.S
+++ b/arch/mips/lib/memcpy.S
@@ -21,7 +21,7 @@
  * end of memory on some systems.  It's also a seriously bad idea on non
  * dma-coherent systems.
  */
-#if !defined(CONFIG_DMA_COHERENT) || !defined(CONFIG_DMA_IP27)
+#ifdef CONFIG_DMA_NONCOHERENT
 #undef CONFIG_CPU_HAS_PREFETCH
 #endif
 #ifdef CONFIG_MIPS_MALTA