[AMDGPU] Fix operands of S_BFE_U64 and S_BFM_B64

src1 of s_bfe_u64 is 32-bit (same as s_bfe_i64).
src0 and src1 of s_bfm_b64 are 32-bit.
Update tests.

Review: http://reviews.llvm.org/D17480

Reviewers: arsenm
llvm-svn: 261621