kmssink: Add support for mxsfb-drm driver

The mxsfb-drm driver has been added to the kernel long ago and will now
be the default display driver for NXP i.MX28, i.MX6SX and i.MX7D
processors so now is a good time to add it to kmssink.

Also, this is used in the upcoming i.MX8MQ and i.MX8MM processors.

https://bugzilla.gnome.org/show_bug.cgi?id=796873
diff --git a/sys/kms/gstkmssink.c b/sys/kms/gstkmssink.c
index 88ef42e..1331883 100644
--- a/sys/kms/gstkmssink.c
+++ b/sys/kms/gstkmssink.c
@@ -168,7 +168,7 @@
 {
   static const char *drivers[] = { "i915", "radeon", "nouveau", "vmwgfx",
     "exynos", "amdgpu", "imx-drm", "rockchip", "atmel-hlcdc", "msm",
-    "xlnx", "vc4", "meson", "sun4i-drm",
+    "xlnx", "vc4", "meson", "sun4i-drm", "mxsfb-drm",
     "xilinx_drm",               /* DEPRECATED. Replaced by xlnx */
   };
   int i, fd = -1;