[xla:gpu] Do not copy constant dynamic-slice offsets from device memory
[xla:gpu] Do not copy constant dynamic-slice offsets from device memory

When dynamic-slice/dynamic-update-slice offset is defined by a constant value there is no need to issue D2H transfer to move it to host, and instead we can use the value known at compile time.

This saves 2 out of 3 memory copies for dot operation inside jax.lax.scan loop.
