enable VDSO globally

Disabled VDSO is a performance killer.
Kodi get stuttering audio playback with a lot
of broken pipe error messages.

target/linux/kernel.config

@@ -28,3 +28,4 @@ CONFIG_DEVMEM=y
 CONFIG_DEVKMEM=y
 CONFIG_EXPERT=y
 CONFIG_MULTIUSER=y
+CONFIG_VDSO=y