IMPALA-5222: don't call Bits::Log2*() functions
Some of gutil's functions are fairly inefficient. We accidentally
regressed this when switching to the new Bits::, and some of the
BufferPool code that was in flight didn't switch over.
This commit switches to calling BitUtil::Log2*() everywhere and makes
sure that those functions are all implemented in an efficient way.
Reviewed-by: Henry Robinson <firstname.lastname@example.org>
Tested-by: Impala Public Jenkins