mtd: nand: pxa3xx-nand: switch to dmaengine

mtd: nand: pxa3xx-nand: switch to dmaengine

Now pxa architecture has a dmaengine driver, remove the access to direct
dma registers in favor of the more generic dmaengine code.

This should be also applicable for mmp and orion, provided they work in
device-tree environment.

This patch also removes the previous hack which was necessary to make
the driver work in a devicetree environment.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Reviewed-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Tested-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
[Brian: fixup use of 'enum dma_transfer_direction']
Signed-off-by: Brian Norris <computersforpeace@gmail.com>