meta-yocto-bsp: workaround the X malfunction on beaglebone

After the change in kernel commit a291b6b3d287 ("ARM: dts:
am335x-boneblack: Add blue-and-red-wiring -property to LCDC node"),
the pixel format we support for 32bit bpp has been changed from
XRGB8888 to XBGR8888. But the fbdev created by modesetting driver use
the XRGB8888 format by default, this causes the X malfunction. There is
no easy way to adjust the pixel format of the fbdev created by the
modesetting driver. So we create a xorg.conf to use the 16bit bpp to
work around this issue.

[YOCTO #11267]

(From meta-yocto rev: 1ef8a9584298a8745a28c0c92fa3ecbf92ffe494)

Signed-off-by: Kevin Hao <kexin.hao@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta-yocto-bsp/recipes-graphics/xorg-xserver/xserver-xf86-config/beaglebone/xorg.conf

@@ -0,0 +1,20 @@
+Section "Monitor"
+        Identifier      "Builtin Default Monitor"
+EndSection
+
+Section "Device"
+        Identifier      "Builtin Default fbdev Device 0"
+        Driver  "modesetting"
+EndSection
+
+Section "Screen"
+        Identifier      "Builtin Default fbdev Screen 0"
+        DefaultDepth    16
+        Device  "Builtin Default fbdev Device 0"
+        Monitor "Builtin Default Monitor"
+EndSection
+
+Section "ServerLayout"
+        Identifier      "Builtin Default Layout"
+        Screen  "Builtin Default fbdev Screen 0"
+EndSection