Improve benchmark scaling mechanism.

[T-J-Teru]

Would be nice to have an improved benchmark scaling mechanism.

Currently we have:

#define REPEAT_FACTOR ((BOARD_REPEAT_FACTOR) >> (CALIB_SCALE))

Where BOARD_REPEAT_FACTOR is either defined in boardsupport.h (per board) or is the constant 4096. The CALIB_SCALE is defined per benchmark, per board in a file calibration within the boards config file, it will be a small number to shift by, if CALIB_SCALE is not otherwise defined, it defaults to 0.

Finally, in each benchmark we do:

#define SCALE_FACTOR    (REPEAT_FACTOR >> NUMBER)

Where NUMBER is an actual integer, specific to each benchmark.

It was suggested that we should replace this whole mechanism with a simpler scheme where on a per board / chip / benchmark basis we specify a single number for each benchmark. The details still need to be worked out a little more.