zeusminer: allow specifying a max clock of 383
util: introduce nearest_pow() to calculate the nearest power of 2
icarus: support work_division other than 1, 2, 4, 8
zeusminer: use nearest_pow() from util.c/h
zuesminer: bugfix: fixed hashrate estimates by specifying proper values for work_division and fpga_count
zeusminer: enable do_icarus_timing so that read_count is automatically optimized by the driver