xserver_xorg-server: Fix compile error for microblaze

Fixes
mipushpxl.c: In function 'miPushPixels':
mipushpxl.c:110:38: error: 'IMAGE_BYTE_ORDER' undeclared (first use in this function)
     if (screenInfo.bitmapBitOrder == IMAGE_BYTE_ORDER)

Patch submitted upstream: https://bugs.freedesktop.org/show_bug.cgi?id=83582



Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>