drivers: net: NET_XGENE should depend on HAS_DMA

If NO_DMA=y:

drivers/built-in.o: In function `xgene_enet_delete_ring':
xgene_enet_main.c:(.text+0x28755a): undefined reference to `dma_free_coherent'
drivers/built-in.o: In function `xgene_enet_setup_tx_desc':
xgene_enet_main.c:(.text+0x287774): undefined reference to `dma_map_single'
xgene_enet_main.c:(.text+0x287780): undefined reference to `dma_mapping_error'
drivers/built-in.o: In function `xgene_enet_tx_completion':
xgene_enet_main.c:(.text+0x2878e6): undefined reference to `dma_unmap_single'
drivers/built-in.o: In function `xgene_enet_refill_bufpool':
xgene_enet_main.c:(.text+0x2879d4): undefined reference to `dma_map_single'
xgene_enet_main.c:(.text+0x2879e0): undefined reference to `dma_mapping_error'
drivers/built-in.o: In function `xgene_enet_rx_frame':
xgene_enet_main.c:(.text+0x287aaa): undefined reference to `dma_unmap_single'
drivers/built-in.o: In function `xgene_enet_free_desc_ring':
xgene_enet_main.c:(.text+0x287f98): undefined reference to `dma_free_coherent'
drivers/built-in.o: In function `xgene_enet_create_desc_ring':
xgene_enet_main.c:(.text+0x28808e): undefined reference to `dma_alloc_coherent'
drivers/built-in.o: In function `xgene_enet_probe':
xgene_enet_main.c:(.text+0x2883d4): undefined reference to `dma_set_mask'
xgene_enet_main.c:(.text+0x2883ec): undefined reference to `dma_supported'

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: David S. Miller <davem@davemloft.net>