Add DMA support to I2S

[calvinatintel]

libarc32drv_arduino101.a updated. Replaces PR #230.
@bigdinotech @linrjing Please give me a good description of the changes to be put into the git commit.

[linrjing]

@calvinatintel The description of the git commit can be "I2S DMA implement: supplement library and example". Now the codes have been updated on my feature/i2s_dma branch, please merge it with your branch. The changes are: (1)combine I2SDMA with the existing I2S library；(2)Tx side does not need to add 2 extra buffer;(3)after TX-DMA transfer completed, 4 zero would be pushed into the TX FIFO to make sure all expected data have been transmitted to RX side.

[linrjing]

@xieqi @sgbhu @SidLeung the original request is closed. Calvin helped make a new one here.

[calvinatintel]

Added the latest change from linrjing.
@bigdinotech Please test. Once it's confirmed to work, I'll squash the two commits into one.

[linrjing]

@calvinatintel @bigdinotech currently the code is only for the sample resolution = 32 bit.

[SidLeung]

@calvinatintel The Flex China team is planning to make the implementation to fix the range the sampling resolutions (24, 16, 8 bits). I suppose it would be cleaner if we first let this commit emerge to the trunk first, fork a branch, implement the extra supporting resolutions, push, and merge again. Please advise.

[calvinatintel]

@SidLeung Would that break the main repo? If you'd like, I can put it on a branch and you can fork that.

[calvinatintel]

About to merge. @bigdinotech Can you confirm?

[bigdinotech]

@calvinatintel ready for merge

[calvinatintel]

Squashed and merged

[SidLeung]

Thanks @calvinatintel and @bigdinotech. Flex China can now do a fork and add in the new implementation..