AMDGPU/SI: Support data types other than V4f32 in image intrinsics

Summary:
  Extend image intrinsics to support data types of V1F32 and V2F32.

  TODO: we should define a mapping table to change the opcode for data type of V2F32 but just one channel is active,
  even though such case should be very rare.

Reviewers:
  tstellarAMD

Differential Revision:
  http://reviews.llvm.org/D26472

llvm-svn: 286860