Variable time resolution in histogram (Jiffy)

Changed variable types to make them more consistent,
e.g., always use int64_t. Made histogram take up less
space by adjusting the column with for each value.
Example of results (only the fastmixer histogram's
left half is shown, not the slowmixer's).

Occurrences
  2    2    2    7   21   44  122  416  394  123

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                 |    |    |    |    |    |    |
  |    |    |    |    |    |    |    |    |    |
  |    |    |    |    |    |    |    |    |    |
 ________________________________________________
3.2  3.3  3.4  3.5  3.6  3.7  3.8  3.9  4.0     ms

Test: dumpsys media.log

Change-Id: I007a6104c3f62ab04ee386a1de196b267adddecc