Add exp2f and log2f benchmark trace

exp2f and log2f benchmark traces are just copies of the existing
expf and logf traces from wrf_r.

	* benchtests/Makefile: Add exp2f and log2f benchmarks.
	* benchtests/exp2f-inputs: Copy of expf-inputs.
	* benchtests/log2f-inputs: Copy of logf-inputs.