x86/speculation: Always disable IBRS in disable_ibrs_and_friends()

x86/speculation: Always disable IBRS in disable_ibrs_and_friends()

Booting with "spectre_v2=retpoline" calls disable_ibrs_and_friends(false),
which does not set ibrs_disabled. Then, when attempting to enable
IBRS by writing 1 to ibrs_enabled, change_spectre_v2_mitigation() is called
and it looks like IBRS is already in use (ibrs_used = !ibrs_disabled) so it
does not activate IBRS.

Because now we use change_spectre_v2_mitigation() to activate IBRS when
using the retpoline fallback mechanism, and this function clears
ibrs_disabled before activating IBRS, we can fix disable_ibrs_and_friends()
and set ibrs_disabled there every time.

Orabug: 29139710

Signed-off-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
Reviewed-by: Mihai Carabas <mihai.carabas@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>