[PATCH v9 0/2] add uart DMA function

[Long Cheng]

In Mediatek SOCs, the uart can support DMA function.
Base on DMA engine formwork, we add the DMA code to support uart. And put the code under drivers/dma.

This series contains document bindings, Kconfig to control the function enable or not,
device tree including interrupt and dma device node, the code of UART DMA

Changes compared to v8
-revise missing items
Changes compared to v7:
-modify apdma uart tx
Changes compared to v6:
-Correct spelling
Changes compared to v5:
-move 'requst irqs' to alloc channel
-remove tasklet.
Changes compared to v4:
-modify Kconfig depends on.
Changes compared to v3:
-fix CONFIG_PM, will cause build fail
Changes compared to v2:
-remove unimportant parameters
-instead of cookie, use APIs of virtual channel.
-use of_dma_xlate_by_chan_id.
Changes compared to v1:
-mian revised file, 8250_mtk_dma.c
--parameters renamed for standard
--remove atomic operation