[NVPTX] Compute 'rem' using the result of 'div', if possible.

Summary:
In isel, transform

  Num % Den

into

  Num - (Num / Den) * Den

if the result of Num / Den is already available.

Reviewers: tra

Subscribers: hfinkel, llvm-commits, jholewinski

Differential Revision: https://reviews.llvm.org/D26090

llvm-svn: 285461