freedreno: add simpler ring-reloc

Provide a way to insert a reference (ie. OUT_IB()) to a target ring,
executing all the cmds in the target ring from the start.

Sometimes the ringmarker stuff is just overkill.  And it will won't
really work properly once we support multiple physical cmdstream buffers
per fd_ringbuffer.  So in the future the old ringmarker related APIs
will be deprecated in a few releases.

Signed-off-by: Rob Clark <robclark@freedesktop.org>