Currently omap2-mcspi cannot handle dma transfer for vmalloced buffer.
I hit this problem when using mtdblock on spi-nor.

This lets the SPI core handle the page mapping for dma transfer buffer.
Signed-off-by: NAkinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: NMark Brown <broonie@kernel.org>