[llvm-mca] Add extra counters for move elimination in view RegisterFileStatistics.

This patch teaches view RegisterFileStatistics how to report events for
optimizable register moves.

For each processor register file, view RegisterFileStatistics reports the
following extra information:
 - Number of optimizable register moves
 - Number of register moves eliminated
 - Number of zero moves (i.e. register moves that propagate a zero)
 - Max Number of moves eliminated per cycle.

Differential Revision: https://reviews.llvm.org/D53976

llvm-svn: 345865