weston: egl requires gles as well

weston: egl requires gles as well

>From configure.ac lines 83-89:

AC_ARG_ENABLE(egl, [  --disable-egl],,
	enable_egl=yes)
AM_CONDITIONAL(ENABLE_EGL, test x$enable_egl = xyes)
if test x$enable_egl = xyes; then
	AC_DEFINE([ENABLE_EGL], [1], [Build Weston with
	EGL support])
	PKG_CHECK_MODULES(EGL, [egl glesv2])
	PKG_CHECK_MODULES([EGL_TESTS], [egl glesv2 wayland-client
	wayland-egl])

It also requires wayland-egl which is only provided by mesa3d for now,
hence make it conditional on mesa3d egl+gles.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>