mesa/main: do not allow stencil-texture enums on gles1

mesa/main: do not allow stencil-texture enums on gles1

ctx->Extensions.ARB_texture_stencil8 is set regardless of the API
that's used, so checking for those direcly will always allow the
enums from this extensions when they are supported by the driver.

So let's instead check for both ARB_texture_stencil8 and
OES_texture_stencil8, so we support depth textures on OpenGL and
OpenGL ES 2.0+. There's no extension enabling stencil-textures for
OpenGL ES 1.x, so we shouldn't allow those enums there.

Signed-off-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>