vl: Add DT_COCOA DisplayType value

Instead of reusing DT_SDL for Cocoa, use DT_COCOA to indicate
that a Cocoa display was requested.

configure already ensures CONFIG_COCOA and CONFIG_SDL are never
set at the same time. The only case where DT_SDL is used outside
a #ifdef CONFIG_SDL block is in the no_frame/alt_grab/ctrl_grab
check. That means the only user-visible change is that we will
start printing a warning if the SDL-specific options are used in
Cocoa mode. This is a bugfix, because no_frame/alt_grab/ctrl_grab
are not used by Cocoa code.

Cc: Andreas Färber <andreas.faerber@web.de>
Cc: Peter Maydell <peter.maydell@linaro.org>
Acked-by: NAndreas Färber <andreas.faerber@web.de>
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>

include/sysemu/sysemu.h

@@ -136,6 +136,7 @@ typedef enum DisplayType
     DT_DEFAULT,
     DT_CURSES,
     DT_SDL,
+    DT_COCOA,
     DT_GTK,
     DT_NOGRAPHIC,
     DT_NONE,

vl.c

@@ -4237,8 +4237,10 @@ int main(int argc, char **argv, char **envp)
     if (display_type == DT_DEFAULT && !display_remote) {
 #if defined(CONFIG_GTK)
         display_type = DT_GTK;
-#elif defined(CONFIG_SDL) || defined(CONFIG_COCOA)
+#elif defined(CONFIG_SDL)
         display_type = DT_SDL;
+#elif defined(CONFIG_COCOA)
+        display_type = DT_COCOA;
 #elif defined(CONFIG_VNC)
         vnc_parse("localhost:0,to=99,id=default", &error_abort);
         show_vnc_port = 1;
@@ -4560,7 +4562,7 @@ int main(int argc, char **argv, char **envp)
         sdl_display_init(ds, full_screen, no_frame);
         break;
 #elif defined(CONFIG_COCOA)
-    case DT_SDL:
+    case DT_COCOA:
         cocoa_display_init(ds, full_screen);
         break;
 #endif