glamor: make use of GL_EXT_texture_format_BGRA8888

For 24 and 32 bit depth pictures xserver uses PICT_x8r8g8b8 and PICT_a8r8g8b8 formats,
which must be backed with GL_BGRA format. It is present in OpenGL ES 2.0 only with
GL_EXT_texture_format_BGRA8888 extension. We require such extension in glamor_init,
so, why not to make use of it?
Fixes #1208
Fixes #1354

Signed-off-by: Konstantin Pugin <ria.freelander@gmail.com>

Reviewed-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Emma Anholt <emma@anholt.net>

test/bugs/meson.build

@@ -45,7 +45,6 @@ if get_option('xvfb')
                     ],
                 suite: 'xephyr-glamor-gles2',
                 timeout: 300,
-                should_fail: true,
             )
     endif
 endif