Description: x86/speculation: Allow enabling STIBP with legacy IBRS
References:
 https://github.com/google/security-research/security/advisories/GHSA-mj4w-6495-6crx
 https://kernel.dance/#6921ed9049bc7457f66c1596c5b78aec0dae4a9d
Notes:
Bugs:
upstream: released (6.3-rc1) [6921ed9049bc7457f66c1596c5b78aec0dae4a9d]
6.1-upstream-stable: released (6.1.16) [08d87c87d6461d16827c9b88d84c48c26b6c994a]
5.10-upstream-stable: released (5.10.173) [abfed855f05863d292de2d0ebab4656791bab9c8]
4.19-upstream-stable: released (4.19.276) [10543fb3c9b019e45e2045f08f46fdf526add593]
sid: released (6.1.20-1)
5.10-bullseye-security: released (5.10.178-1)
4.19-buster-security: released (4.19.282-1)