configure.ac: The drm backend no longer requires EGL

We can run with just the pixman renderer and 'dumb' kms buffers.
diff --git a/configure.ac b/configure.ac
index 90b0c81..a460d3b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -143,8 +143,8 @@
 
 AC_ARG_ENABLE(drm-compositor, [  --enable-drm-compositor],,
 	      enable_drm_compositor=yes)
-AM_CONDITIONAL(ENABLE_DRM_COMPOSITOR, test x$enable_drm_compositor = xyes -a x$enable_egl = xyes)
-if test x$enable_drm_compositor = xyes -a x$enable_egl = xyes; then
+AM_CONDITIONAL(ENABLE_DRM_COMPOSITOR, test x$enable_drm_compositor = xyes)
+if test x$enable_drm_compositor = xyes; then
   AC_DEFINE([BUILD_DRM_COMPOSITOR], [1], [Build the DRM compositor])
   PKG_CHECK_MODULES(DRM_COMPOSITOR, [libudev >= 136 libdrm >= 2.4.30 gbm mtdev >= 1.1.0])
 fi