[Backport to server-21.1-branch] 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 (closed) Fixes #1354 (closed)

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

Reviewed-by: Adam Jackson ajax@redhat.com Reviewed-by: Emma Anholt emma@anholt.net (cherry picked from commit 24cd5f34)