librem5-wayland: Default to OpenGLES

Otherwise gstreamer prefers GL over GLES and e.g. the hantro pipeline

   GST_DEBUG=3 gst-launch-1.0 filesrc location=foo.mkv ! parsebin ! v4l2slh264dec ! glimagesink

fails like

   0:00:00.437943323  3672 0xaaaaebf2a6a0 WARN                    glsl gstglsl.c:546:gst_gl_version_to_glsl_version: unknown GL version
   0:00:00.438048688  3672 0xaaaaebf2a6a0 ERROR              glslstage gstglslstage.c:345:gst_glsl_stage_set_strings:<glslstage0> GL context does not support version 110 and profile compatibility
   0:00:00.438087810  3672 0xaaaaebf2a6a0 ERROR              glconvert gstglcolorconvert.c:2045:_create_shader:<glcolorconvert0> Failed to create vertex stage
   0:00:00.438143972  3672 0xffff90002240 WARN        glconvertelement gstglcolorconvertelement.c:224:gst_gl_color_convert_element_prepare_output_buffer:<glcolorconvertelement0> error: Failed to convert video buffer
3 jobs for gst-gl in 3 minutes and 58 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Package
passed #331052
librem5
package:deb-debian

00:00:41

 
  Test Package
passed #331053
librem5
autopkgtest-debian-package

00:03:16

passed #331054
librem5
lintian-debian-package

00:00:34