[xla:gpu] Fix the dimension order propagation for bitcast
[xla:gpu] Fix the dimension order propagation for bitcast

If bitcast's destination contains a trivial dimension, it will create an unnecessary trivial fragment after propagation. For example:

%p = f32[5,1] parameter(0)
%bitcast = f32[5] bitcast(%p)

When propagating dimension order from bitcast to p, it creates a fragment of size 1 for %p.
