R600: Factor i64 UDIVREM lowering into its own fuction

This is so it could potentially be used by SI.  However, the current
implementation does not always produce correct results, so the
IntegerDivisionPass is being used instead.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222072 91177308-0d34-0410-b5e6-96231b3b80d8
R600: Fix 64-bit integer division

This fixes a failure in one of the oclconform tests.

Patch by: Jan Vesely

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222073 91177308-0d34-0410-b5e6-96231b3b80d8