mtd: rawnand: gpmi: drop dma_ops_type

The GPMI nand driver puts dma_ops_type in its private data struct. Based
on the ops type the DMA callback handler unmaps previously mapped
buffers. Instead of unmapping the buffers in the DMA callback handler,
do this in the caller directly which waits for the DMA transfer to
finish. This makes the whole dma_ops_type mechanism unnecessary.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>