Display detailed profile summary in llvm-profdata tool.

This adds a detailed profile summary in llvm-profdata. The summary is in the
form of one or more triples of the form (P, N, M) which is interpreted as if
we look at the Top-N counts in the profile, their sum accounts for P percentage
of the sum of all counts in the program and the minimum count in the Top-N is M.

Differential Revision: http://reviews.llvm.org/D16005

llvm-svn: 257680