Handle all live physreg defs in the same place.

SelectionDAG has 4 different ways of passing physreg defs to users.
Collect all of the uses at the same time, and pass all of them to
MI->setPhysRegsDeadExcept() to mark the remaining defs dead.

The setPhysRegsDeadExcept() function will soon add the required
implicit-defs to instructions with register mask operands.

llvm-svn: 149708