This patch add two benchmarks for both expf and exp2f, one which
measures thoughput, as default, and one which measures latency. The
latency benchmark works by creating a dependency on the previous
iteration and with a zero multiply to avoid changing the input value.
The input is based on a reduced trace based on 2.4 billion samples
extracted from specpu2017 521.wrf_r benchmark.
Test: ran 32-bit and 64-bit x86 tests on host
Change-Id: Ic0d40cc4977dd6875fb7431146fc38ea0e6e0bc2
