Limit runtime determined PTX version by compile time CUDA version
Limit runtime determined PTX version by compile time CUDA version

The previously introduced new PTX version logic determines
the supported PTX version based on the `ptxas` tool version at runtime.

If a user has a CUDA toolkit installed that is newer than what
XLA was compiled with we might set a PTX version that is not
supported by XLA/LLVM.

To avoid that this change determines the PTX version from the
minimum of both the compile time and the runtime CUDA version.
