Hexagon: list available CPUs with -cpu help

Currently, qemu-hexagon only models the v67 cpu. Nonetheless if we try
to get this information with `-cpu help`, qemu just exists with an error
code and no output. Let's correct that.

The code is basically a copy from target/alpha/cpu.h, but we strip the
"-hexagon-cpu" suffix before printing. This is to avoid confusing
situations like the following:

    $ qemu-hexagon -cpu help

    Available CPUs:
      v67-hexagon-cpu

    $ qemu-hexagon -cpu v67-hexagon-cpu ./prog

    qemu-hexagon: unable to find CPU model 'v67-hexagon-cpu'

Signed-off-by: Matheus Tavares Bernardino <quic_mathbern@quicinc.com>
Signed-off-by: Taylor Simpson <tsimpson@quicinc.com>
Tested-by: Taylor Simpson <tsimpson@quicinc.com>
Reviewed-by: Taylor Simpson <tsimpson@quicinc.com>
Message-Id: <b946e17c7e17eed9095700b54c5ead36e5d55dfa.1683225804.git.quic_mathbern@quicinc.com>

target/hexagon/cpu.c

@@ -31,6 +31,26 @@ static void hexagon_v69_cpu_init(Object *obj) { }
 static void hexagon_v71_cpu_init(Object *obj) { }
 static void hexagon_v73_cpu_init(Object *obj) { }
 
+static void hexagon_cpu_list_entry(gpointer data, gpointer user_data)
+{
+    ObjectClass *oc = data;
+    char *name = g_strdup(object_class_get_name(oc));
+    if (g_str_has_suffix(name, HEXAGON_CPU_TYPE_SUFFIX)) {
+        name[strlen(name) - strlen(HEXAGON_CPU_TYPE_SUFFIX)] = '\0';
+    }
+    qemu_printf("  %s\n", name);
+    g_free(name);
+}
+
+void hexagon_cpu_list(void)
+{
+    GSList *list;
+    list = object_class_get_list_sorted(TYPE_HEXAGON_CPU, false);
+    qemu_printf("Available CPUs:\n");
+    g_slist_foreach(list, hexagon_cpu_list_entry, NULL);
+    g_slist_free(list);
+}
+
 static ObjectClass *hexagon_cpu_class_by_name(const char *cpu_model)
 {
     ObjectClass *oc;

target/hexagon/cpu.h

@@ -48,6 +48,9 @@
 #define TYPE_HEXAGON_CPU_V71 HEXAGON_CPU_TYPE_NAME("v71")
 #define TYPE_HEXAGON_CPU_V73 HEXAGON_CPU_TYPE_NAME("v73")
 
+void hexagon_cpu_list(void);
+#define cpu_list hexagon_cpu_list
+
 #define MMU_USER_IDX 0
 
 typedef struct {