[AMDGPU] Change llvm.amdgcn.image.bvh.intersect.ray to take vec3 args

[AMDGPU] Change llvm.amdgcn.image.bvh.intersect.ray to take vec3 args

The ray_origin, ray_dir and ray_inv_dir arguments should all be vec3 to
match how the hardware instruction works.

Don't change the API of the corresponding OpenCL builtins.

Differential Revision: https://reviews.llvm.org/D115032