R600/SI: Add pattern for bitcasting fp immediates to integers

R600/SI: Add pattern for bitcasting fp immediates to integers

The backend now assumes that all immediates are integers.  This allows
us to simplify immediate handling code, becasue we no longer need to
handle fp and integer immediates differently.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225844 91177308-0d34-0410-b5e6-96231b3b80d8