refactor ceil/floor log2 handling

• create ceilLog2() function based on floorLog2
• use intrinsics for MSVC in floorLog2
• replace all ceil(log2()) calls in HLS with ceilLog2()
• replace g_aucLog2[] with floorLog2

First test results indicate no change in coding performance, maybe slightly longer run times (but could be jitter on the cluster).