nios2: remove unneeded HAS_DMA define

kernel/dma/Kconfig globally defines HAS_DMA as follows:

  config HAS_DMA
          bool
          depends on !NO_DMA
          default y

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
diff --git a/arch/nios2/Kconfig b/arch/nios2/Kconfig
index f6c4b0f..532343e 100644
--- a/arch/nios2/Kconfig
+++ b/arch/nios2/Kconfig
@@ -36,9 +36,6 @@
 config NO_IOPORT_MAP
 	def_bool y
 
-config HAS_DMA
-	def_bool y
-
 config FPU
 	def_bool n