Pull DMA mapping updates from Christoph Hellwig:

 - remove the already broken support for NULL dev arguments to the DMA
   API calls

 - Kconfig tidyups

* tag 'dma-mapping-5.2' of git://git.infradead.org/users/hch/dma-mapping:
  dma-mapping: add a Kconfig symbol to indicate arch_dma_prep_coherent presence
  dma-mapping: remove an unnecessary NULL check
  x86/dma: Remove the x86_dma_fallback_dev hack
  dma-mapping: remove leftover NULL device support
  arm: use a dummy struct device for ISA DMA use of the DMA API
  pxa3xx-gcu: pass struct device to dma_mmap_coherent
  gbefb: switch to managed version of the DMA allocator
  da8xx-fb: pass struct device to DMA API functions
  parport_ip32: pass struct device to DMA API functions
  dma: select GENERIC_ALLOCATOR for DMA_REMAP