[llvm-profdata] add value-cutoff functionality in show command

This patch improves llvm-profdata show command:
(1) add -value-cutoff=<N> option: Show only those functions whose max count
    values are greater or equal to N.
(2) add -list-below-cutoff option: Only output names of functions whose max
    count value are below the cutoff.
(3) formats value-profile counts and prints out percentage.

Differential Revision: https://reviews.llvm.org/D56342

llvm-svn: 350673