mesa: enable EXT_render_snorm extension

mesa: enable EXT_render_snorm extension

Patch sets additional formats renderable and enables the extension
when OpenGL ES 3.1 is supported.

v2: instead of dummy_true, have a separate toggle for extension
    (Eric Anholt)

v3: add missing checks, simplify some existing checks and fix
    glCopyTexImage2D check (Nanley Chery)

    add SHORT and BYTE support in read_pixels_es3_error_check

Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Nanley Chery <nanley.g.chery@intel.com>