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: NMasahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>

arch/nios2/Kconfig

@@ -36,9 +36,6 @@ config GENERIC_CALIBRATE_DELAY
 config NO_IOPORT_MAP
 	def_bool y
 
-config HAS_DMA
-	def_bool y
-
 config FPU
 	def_bool n