sh4: simplify superh_cpu_class_by_name()

currently for sh4 cpu_model argument for '-cpu' option
could be either 'cpu model' name or cpu_typename.

however typically '-cpu' takes 'cpu model' name and
cpu type for sh4 target isn't advertised publicly
('-cpu help' prints only 'cpu model' names) so we
shouldn't care about this use case (it's more of a bug).

1. Drop '-cpu cpu_typename' to align with the rest of
   targets.
2. Compose searched for typename from cpu model and use
   it with object_class_by_name() directly instead of
   over-complicated
       object_class_get_list()
       g_slist_find_custom() + superh_cpu_name_compare()

With #1 droped, #2 could be used for both lookups which
simplifies superh_cpu_class_by_name() quite a bit.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Acked-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <1507211474-188400-23-git-send-email-imammedo@redhat.com>
[ehabkost: Include fixup sent by Igor]
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

linux-user/main.c

@@ -4331,7 +4331,7 @@ int main(int argc, char **argv, char **envp)
         cpu_model = "750";
 # endif
 #elif defined TARGET_SH4
-        cpu_model = TYPE_SH7785_CPU;
+        cpu_model = "sh7785";
 #elif defined TARGET_S390X
         cpu_model = "qemu";
 #else