target-i386: Move cpu_x86_init()

Consolidate CPU functions in cpu.c.
Allows to make cpu_x86_register() static.

No functional changes.

Signed-off-by: Andreas Färber <afaerber@suse.de>
target-i386: Split command line parsing out of cpu_x86_register()

In order to instantiate a CPU subtype we will need to know which type,
so move the cpu_model splitting into cpu_x86_init().

Parameters need to be set on the X86CPU instance, so move
cpu_x86_parse_featurestr() into cpu_x86_init() as well.

This leaves cpu_x86_register() operating on the model name only.

Signed-off-by: Andreas Färber <afaerber@suse.de>
target-i386: Prepare class lookup

Signed-off-by: Andreas Färber <afaerber@suse.de>
target-i386: Slim conversion to X86CPU subclasses

Signed-off-by: Andreas Färber <afaerber@suse.de>