Rust examples enable bit manipulation extension, but unsupported by CPU

[jbeaurivage]

The Rust examples currently enable the bit manipulation extensions in the compiler target features:

rustflags = ["-Ctarget-feature=+zba,+zbb,+zbc,+zbs"]

However the Ibex demo system disables the bit manipulation extension in the CPU. This leads to the compiled examples emitting unsupported instructions, leading to surprising results.

Would it be preferable to disable the bitmanip features in the examples, or enable them in the demo system's CPU?

[marnovandermaas]

Good point, feel free to open a pull request disabling the bit manipulation extension.