We check the availability of dma_mmap_coherent() in hw_support_mmap()
but with an ugly ifdef of lots of arch-checks.  Now we have a nice
CONFIG_ARCH_NO_COHERENT_DMA_MMAP kconfig, and this can be used
together with CONFIG_HAS_DMA check for a cleaner and more
comprehensive check.
Signed-off-by: Takashi Iwai <tiwai@suse.de>