staging: mt7621-mmc: MIPS: ralink: add sdhci for mt7620a SoC

staging: mt7621-mmc: MIPS: ralink: add sdhci for mt7620a SoC

NeilBrown:
  Added range-check on pdev->id before assigning ot
    host->id

  of_dma_configure() sets a default ->dma_mask of
  DMA_BIT_MASK(32), claiming devices can DMA from
  the full 32bit address space.
  The mtk-mmc driver does not support access to
  highmem pages, so it is really limited to the
  bottom 512M (actually 448M due to 64M of IO space).
  Setting ->dma_mask to NULL causes mmc_setup_queue()
  to fall-back to using BLK_BOUNCE_HIGH to tell the
  block layer to use a bounce-buffer for any highmem
  pages requiring IO.

Signed-off-by: John Crispin <blogic@openwrt.org>
Signed-off-by: NeilBrown <neil@brown.name>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>