TODO for slave dma

1. Move remaining drivers to use new slave interface
2. Remove old slave pointer machansim
3. Make issue_pending to start the transaction in below drivers
	- mpc512x_dma
	- imx-dma
	- imx-sdma
	- mxs-dma.c
	- dw_dmac
	- intel_mid_dma
	- ste_dma40
4. Check other subsystems for dma drivers and merge/move to dmaengine
5. Remove dma_slave_config's dma direction.