mtd: onenand: omap2: Simplify the DMA setup for various paths

We have 4 functions containing almost identical DMA setup code. Create one
function which can set up the DMA for both read and write and use this in
place for the setup code in the driver.
The new function will use wait_for_completion_io_timeout() and it will
figure out the best data_type to be used for the transfer instead of
hardwiring 32 or 16 bit data.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Ladislav Michl <ladis@linux-mips.org>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
Acked-by: Roger Quadros <rogerq@ti.com>
Tested-by: Tony Lindgren <tony@atomide.com>
Tested-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>