drm/i915: Generalize the CRC command format for future work

Let's move from writing 'A plane1' to 'pipe A plane1' to
i915_pipe_crc_ctl. This will allow us to extend the interface to
transcoders or DDIs in the future.

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>