[AArch64] Update successor probabilities after ccmp-conversion

This patch modifies the conditional compares pass so that it keeps successor
probabilities up-to-date after the conversion. Previously, successor
probabilities were being normalized to a uniform distribution, even though they
may have been heavily biased prior to the conversion (e.g., if one of the edges
was the back edge of a loop). This loss of information affected passes later in
the pipeline.

Differential Revision: https://reviews.llvm.org/D34109

llvm-svn: 306412