x86/speculation: Dynamic enable and disable of RSB stuffing with IBRS&!SMEP

x86/speculation: Dynamic enable and disable of RSB stuffing with IBRS&!SMEP

As IBRS is a dynamic feature, RSB overwrite needs to also be dynamically
activated and disabled with IBRS (if SMEP is not available).

Signed-off-by: William Roche <william.roche@oracle.com>
Co-developed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
(cherry picked from commit fe61cd8181780903b2e092e2079ee09a6eb733d9)

Orabug: 29660924

Signed-off-by: William Roche <william.roche@oracle.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Acked-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>
Conflicts:
	arch/x86/kernel/cpu/bugs.c
	arch/x86/kernel/cpu/spec_ctrl.c
bugs.c vs bugs_64.c in UEK4
spec_ctrl.c code still in bugs_64.c on UEK4

Signed-off-by: Brian Maly <brian.maly@oracle.com>