Write recognized CPUID flags into static file

Write recognized CPUID flags into static file

located at /usr/share/kvm/recognized-CPUID-flags-x86_64

It's a simple one flag per line list of all flags the build of QEMU
can understand for x86_64 CPUs.

It will be used in qemu-server for the custom CPU model feature.

For now, only x86_64 is implemented, since aarch64 doesn't print any flags when
called this way.

Co-developed-by: Stefan Reiter <s.reiter@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>