redhat: switch the vsyscall config to CONFIG_LEGACY_VSYSCALL_XONLY=y

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2023041 Upstream Status: RHEL only

This change is being done also on Fedora, requested through this Fedora bug: https://bugzilla.redhat.com/show_bug.cgi?id=1876977

As discussed upstream eg. at: https://lore.kernel.org/linux-api/87h7bzjaer.fsf@oldenburg.str.redhat.com/T/

And as pointed on the Fedora bug's description above, VSYSCALL_XONLY is more secure while still maintaining useful backward compatibility. This was also discussed on the RHEL bug above and the conclusion is to switch to VSYSCALL_XONLY.

v2: move the CONFIG_LEGACY_VSYSCALL* files to the x86 directory, as they are x86 only settings, as reported/suggested by Waiman Long.

Signed-off-by: Herton R. Krzesinski herton@redhat.com