freedreno: Re-work fd_submit fence interface

freedreno: Re-work fd_submit fence interface

Move everything into a struct assocated with the pipe_fence_handle, so
that the drm layer can fill in the seqn/fd fences directly.

This will give us a comvenient place to insert a util_queue_fence in the
next commit.

While we're at it, extract the uint32_t fence (previously called
'timestamp' in place, a kgsl legacy) into a struct that encapsulates
both the kernel fence and the userspace fence.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10444>