x86/CPU: Add support for Vortex CPUs

DM&P devices were not being properly identified, which resulted in
unneeded Spectre/Meltdown mitigations being applied.

The manufacturer states that these devices execute always in-order and
don't support either speculative execution or branch prediction, so
they are not vulnerable to this class of attack. [1]

This is something I've personally tested by a simple timing analysis
on my Vortex86MX CPU, and can confirm it is true.

Add identification for some devices that lack the CPUID product name
call, so they appear properly on /proc/cpuinfo.

¹https://www.ssv-embedded.de/doks/infos/DMP_Ann_180108_Meltdown.pdf

[ bp: Massage commit message. ]

Signed-off-by: Marcos Del Sol Vives <marcos@orca.pet>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211017094408.1512158-1-marcos@orca.pet