llvmpipe: do not enable tessellation shader without llvm coroutines support

llvmpipe: do not enable tessellation shader without llvm coroutines support

Tessellation shader in llvmpipe depends on llvm coroutines support. So do not
advertise tessellation shader support in llvmpipe if GALLIVM_HAVE_CORO is FALSE.

This fixes assertion in LLVMTokenTypeInContext() running tessellation shader
tests with llvm version < 6.

Fixes: eb522717 "llvmpipe: add support for tessellation shaders"
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Neha Bhende <bhenden@vmware.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5366>