octeontx2-af: Fix PF driver crash with kexec kernel booting

In the Linux kernel, the following vulnerability has been resolved: octeontx2-af: Fix PF driver crash with kexec kernel booting During a kexec reboot the hardware is not power-cycled, so AF state from the old kernel can persist into the new kernel. When AF and PF drivers are built as modules, the PF driver may probe before AF reinitializes the hardware. The PF driver treats the RVUM block revision as an indication that AF initialization is complete. If this value is left uncleared at shutdown, PF may incorrectly assume AF is ready and access stale hardware state, leading to a crash. Clear the RVUM block revision during AF shutdown to avoid PF mis-detecting AF readiness after kexec.