mi: move over mioverlay.c to hw/xfree86/compat

Since these are just dummies needed for compat with proprietary
Nvidia driver, they're better off in the compat directory.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>

hw/xfree86/compat/meson.build

@@ -1,6 +1,7 @@
 srcs_xorg_compat = [
     'clientexception.c',
     'log.c',
+    'mioverlay.c',
     'nvidiabug.c',
     'ones.c',
     'xf86Helper.c',

mi/meson.build

@@ -9,7 +9,6 @@ srcs_mi = [
     'mifillarc.c',
     'migc.c',
     'miglblt.c',
-    'mioverlay.c',
     'mipointer.c',
     'mipoly.c',
     'mipolypnt.c',