BIOS now sets the x2apic enabled bit (and the ACPI table) for extended
APIC modes. Use that bit to indicate if extended mode is set.

 [ bp: Fixup subject prefix, merge subsequent fix
   https://lkml.kernel.org/r/20210415220626.223955-1-mike.travis@hpe.com ]
Signed-off-by: Mike Travis <mike.travis@hpe.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210408160047.1703-1-mike.travis@hpe.com