compositor: migrate to stable viewporter.xml

Migrate from wl_scaler to wp_viewporter extension. The viewporter.xml
file is provided by wayland-protocols.

This stops Weston from advertising wl_scaler, and advertises
wp_viewporter instead.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Bryce Harrington <bryce@osg.samsung.com>
[Pekka: fix wayland-protocols requirement]
diff --git a/configure.ac b/configure.ac
index 2be2277..241c722 100644
--- a/configure.ac
+++ b/configure.ac
@@ -186,7 +186,7 @@
 PKG_CHECK_MODULES(LIBINPUT_BACKEND, [libinput >= 0.8.0])
 PKG_CHECK_MODULES(COMPOSITOR, [$COMPOSITOR_MODULES])
 
-PKG_CHECK_MODULES(WAYLAND_PROTOCOLS, [wayland-protocols >= 1.2],
+PKG_CHECK_MODULES(WAYLAND_PROTOCOLS, [wayland-protocols >= 1.4],
 		  [ac_wayland_protocols_pkgdatadir=`$PKG_CONFIG --variable=pkgdatadir wayland-protocols`])
 AC_SUBST(WAYLAND_PROTOCOLS_DATADIR, $ac_wayland_protocols_pkgdatadir)