Backport f79936545fb12 ("x86/sev-es: Allow copy_from_kernel_nofault() in earlier boot")

commit f79936545fb122856bd78b189d3c7ee59928c751 upstream.

This patch fixes a boot failure that happens with VMs running with SEV-ES or SEV-SNP when the guest kernel is compiled with a gcc version past 12.3 (or possibly earlier) due to undefined behavior. As far as I know, the UB has existed ever since SEV-ES guest support was merged in (I believe 5.9), but only started causing boot failures with the updated compiler. Thus, I propose backporting this patch to stable branches since 5.9.