target-i386: Change CPUID model of 486 to 8

target-i386: Change CPUID model of 486 to 8

This changes the model number of 486 to 8 (DX4) which matches the
feature set presented, and actually has the CPUID instruction.

This adds a compatibility property, to keep model=0 on pc-*-1.4 and older.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
[AF: Add compat_props entry]
Tested-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>