dtrace: implement llquantize log/linear aggregation

dtrace: implement llquantize log/linear aggregation

DTrace offers a histogram aggregation, quantize(), whose bins are base-2
logarithmic.  It also has a linear function lquantize().

Linux DTrace should also implement a log-linear function llquantize().
Such functionality is supported by Solaris DTrace and other tracing tools.
Motivations for such a function include:
  - a logarithmic aggregation with base other than 2 (e.g. base 10)
  - finer control than simply logarithmic
  - greater dynamic range than simply linear

Orabug: 26675659

Signed-off-by: Eugene Loh <eugene.loh@oracle.com>
Reviewed-by: Tomas Jedlicka <tomas.jedlicka@oracle.com>