ASoC: Intel: Remove support for Intel MID DMA from firmware loader

Intel MID DMA driver is going to be removed by the coming commit
36111da7 ("dmaengine: intel-mid-dma: remove the driver") in spi.git
tree. Since there are no users for SST_DMA_TYPE_MID type the support for it
can be removed from here in advance.

Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>