redhat/configs: For aarch64/RT, default kstack randomization off

Unlike other architectures which use their cycles counters to seed the kstack randomization (which is sketchy) aarch64 uses the kernel random number generator. For a list of reasons starting with the lack of an enabled/fast cycle counter, a ubiquitous high frequency timer, nor machines which have the v8.5 FEAT_RNG.

Using the kernel rng is largely an acceptable solution except for RT workloads which can experience quite large latency spikes as a result.

So, lets invert the default kstack randomization for RT kernels on aarch64 until FEAT_RNG is common or a better solution is found.

Signed-off-by: Jeremy Linton jlinton@redhat.com