Refactored several benchmarks to have a consistent structure.

All benchmarks now have a main benchmark function, and similar main
functions which just initialise the board/triggers and call the
benchmark.

    * src/2dfir/fir2dim.c: Refactored code into a benchmark function.
    * src/blowfish/bf.c: Likewise
    * src/bs/bs.c: Likewise
    * src/compress/compress.c: Likewise
    * src/crc32/crc_32.c: Likewise
    * src/cubic/basicmath_small.c: Likewise
    * src/dhrystone/dhry_1.c: Likewise
    * src/dijkstra/dijkstra_small.c: Likewise
    * src/fasta/fasta.c: Likewise
    * src/fdct/fdct.c: Likewise
    * src/matmult/matmult.c: Likewise
    * src/nbody/nbody.c: Likewise
    * src/nettle-cast128/cast128.c: Likewise
    * src/rijndael/aesxam.c: Likewise
    * src/sha/sha_driver.c: Likewise
    * src/whetstone/whetstone.c: Likewise