x86/speculation: functions for supporting enhanced IBRS

x86/speculation: functions for supporting enhanced IBRS

Indirect Branch Restricted Speculation (IBRS) is available either
with a basic support (basic IBRS) or with an enhanced support
(enhanced IBRS). Currently only basic IBRS is implemented, and it
requires IBRS to be set after every transition to a more privileged
predictor mode.

Enhanced IBRS supports an 'always on' model in which IBRS is enabled
once and never disabled. We enhance the existing functions, introduce
new identifiers, and rename existing ones in order to be able to
differentiate between basic and enhanced IBRS.

Signed-off-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
Co-developed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
(cherry picked from commit d762c3e419e1df1e7671c346ab4247a495fbc3dd from UEK5)

Orabug: 28474851

Signed-off-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>
Conflicts:
	arch/x86/include/asm/spec_ctrl.h
(Differences in the IBRS related macro definitions. Not adding
spec_ctrl_flush_all_cpus() that is already in bugs_64.c. Change
set_ibrs_inuse() return value from boolean to void.)

	arch/x86/kernel/cpu/bugs.c
(UEK4 uses bugs_64.c. Slight differences in
disable_ibrs_and_friends() and cpu_show_common().)

	arch/x86/kernel/cpu/spec_ctrl.c
(No need to remove the spec_ctrl_flush_all_cpus(), it is in bugs_64.c)

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