x86/speculation: STUFF_RSB dynamic enable

x86/speculation: STUFF_RSB dynamic enable

The STUFF_RSB overwrite macro can be enabled dynamically with
rsb_overwrite_key instead of using X86_FEATURE_STUFF_RSB.

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 84e09871beb92364bd374d8c3bc3441a8c4be593)

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/include/asm/cpufeatures.h
	arch/x86/include/asm/spec_ctrl.h
	arch/x86/kernel/cpu/bugs.c
cpufeatures.h vs cpufeature.h in UEK4
include <linux/jump_label.h> header in spec_ctrl.h to use this feature
bugs.c vs bugs_64.c in UEK4

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