freedreno: revert bad freedreno/atomic_ops commits

This reverts 6d237985 "xf86atomic: #undef internal define"
and b541d21a "freedreno: remove always-defined #ifdef".

I didn't realise at the time that freedreno/freedreno_ringbuffer.h gets
installed, and then used by Mesa for instance. These two commits were
fine in libdrm, but broke Mesa which needs to use struct fd_ringbuffer
but doesn't need to access ::refcnt. The hack that I removed serves to
keep the struct at the correct size while only exposing the ::refcnt
member within libdrm.

Fixes: 6d237985 "xf86atomic: #undef internal define"
Fixes: b541d21a "freedreno: remove always-defined #ifdef"
Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>