[AMDGPU] Combine and x, (sext cc from i1) => select cc, x, 0

Also factored out function to check if a boolean is an already
deserialized value which does not require v_cndmask_b32 to be
loaded. Added binary logical operators to its check.

Differential Revision: https://reviews.llvm.org/D34500

llvm-svn: 306439