xf86-video-glamo: add xserver-xorg-module-exa to RDEPENDS

* it was separated from xserver-xorg package and glamo fails in runtime without that
  http://git.openembedded.org/openembedded-core/commit/?id=1a666ee1cda3c0b74daba5881fc5f62e13deec66



Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>