drm/imx: ipu-v3 fixups and grayscale support

- Make const interrupt register arrays static, reduces object size.
- Fix device_node leaks in PRE/PRG phandle lookup functions.
- Add 8-bit and 16-bit grayscale buffer support to ipu_cpmem_set_image,
- add 10-bit and 12-bit grayscale media bus support to ipu-csi,
  to be used by the imx-media driver.
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