drm: DRM should depend on HAS_DMA

If NO_DMA=y:

drivers/built-in.o: In function `__drm_pci_free':
drivers/gpu/drm/drm_pci.c:112: undefined reference to `dma_free_coherent'
drivers/built-in.o: In function `drm_pci_alloc':
drivers/gpu/drm/drm_pci.c:72: undefined reference to `dma_alloc_coherent'
drivers/built-in.o: In function `drm_gem_unmap_dma_buf':
drivers/gpu/drm/drm_prime.c:87: undefined reference to `dma_unmap_sg'
drivers/built-in.o: In function `drm_gem_map_dma_buf':
drivers/gpu/drm/drm_prime.c:78: undefined reference to `dma_map_sg'

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>