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

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

ctx->Extensions.OES_texture_float 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.

There's no extension enabling floating-point 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>