spi: dw-mid: move to use core SPI DMA mappings

SPI core has a comprehensive function set to map and unmap a message when it's
needed. This patch converts driver to use that advantage.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --cc drivers/spi/spi-dw-mid.c
Simple merge

diff --cc drivers/spi/spi-dw.c
Simple merge

diff --cc drivers/spi/spi-dw.h
Simple merge