Linux 6.7.3 + 545.29.06/550.40.07: ERROR: modpost: GPL-incompatible module nvidia.ko uses GPL-only symbol '__rcu_read_lock'

For those that do not want to wait for NVIDIA’s fixed releases, I wrote a quick workaround patch for Gentoo that does not need to modify the kernel.

Not very tested but not seeing how it could cause problems (well, it lacks the kernel’s race fix but should be no worse than it was before and that may not have affected nvidia either way).

Patch was based on 470 but can be applied up to 550 with fuzz 1. Legacy (unsupported) 390 should be fine without this for most given pfn_valid() is only used on ppc64 there.