mmc: sdhci: Add tracepoints to enhance debugging

Instrument the sdhci driver with tracepoints to aid in
debugging issues and identifying latencies in the following
path:
* CMD completion
* DATA completion
* DMA preparation
* Post DMA cleanup

Change-Id: Ie8cd0c2fb6c1bd6ab13883123be021081f8b8f78
Signed-off-by: Venkat Gopalakrishnan <venkatg@codeaurora.org>