package/x11r7/xserver_xorg-server: glamor support needs egl

package/x11r7/xserver_xorg-server: glamor support needs egl

Glamor support in xserver_xorg-server depends on gbm:
https://cgit.freedesktop.org/xorg/xserver/tree/configure.ac#n2100

Gbm is provided by mesa3d only if egl is enabled:
https://git.buildroot.net/buildroot/tree/package/mesa3d/mesa3d.mk#n167

This patch adds libegl as additional prerequisite for enabling glamor
support in xserver_xorg-server.

Fixes
http://autobuild.buildroot.net/results/04d/04d93745d63fcfbea070c0126862b49f1b6f473e/

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>