target/i386: Set family/model/stepping of the "max" CPU according to LM bit

target/i386: Set family/model/stepping of the "max" CPU according to LM bit

We want to get rid of the "#ifdef TARGET_X86_64" compile-time switch
in the long run, so we can drop the separate compilation of the
"qemu-system-i386" binary one day - but we then still need a way to
run a guest with max. CPU settings in 32-bit mode. So the "max" CPU
should determine its family/model/stepping settings according to the
"large mode" (LM) CPU feature bit during runtime, so that it is
possible to run "qemu-system-x86_64 -cpu max,lm=off" and still get
a sane family/model/stepping setting for the guest CPU.

To be able to check the LM bit, we have to move the code that sets
up these properties to a "realize" function, since the LM setting is
not available yet when the "instance_init" function is being called.

Message-Id: <20230306154311.476458-1-thuth@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>