target-i386: Separate feature string parsing from CPU model lookup

target-i386: Separate feature string parsing from CPU model lookup

Instead of parsing the whole cpu_model string inside
cpu_x86_find_by_name(), first split it into the CPU model name and the
full feature string, then parse the feature string into pieces.

When using CPU model classes, those two pieces of information will be
used at different moments (CPU model name will be used to find CPU
class, feature string will be used after CPU object was created), so
making the split in two steps will make it easier to refactor the code
later.

This should also help on the CPU properties work, that will just need to
replace the cpu_x86_parse_featurestr() logic (and can keep the CPU model
lookup code as-is).

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>