drm/imagination/uapi: Add PowerVR driver UAPI

Add the UAPI implementation for the PowerVR driver.

Changes from v8:
- Fixed documentation for unmapping, which previously suggested the
  size was not used
- Corrected license identifier

Changes from v7:
- Remove prefixes from DRM_PVR_BO_* flags
- Improve struct drm_pvr_ioctl_create_hwrt_dataset_args documentation
- Remove references to static area carveouts
- CREATE_BO ioctl now returns an error if provided size isn't page aligned
- Clarify documentation for DRM_PVR_STATIC_DATA_AREA_EOT

Changes from v6:
- Add padding to struct drm_pvr_dev_query_gpu_info
- Improve BYPASS_CACHE flag documentation
- Add SUBMIT_JOB_FRAG_CMD_DISABLE_PIXELMERGE flag

Changes from v4:
- Remove CREATE_ZEROED flag for BO creation (all buffers are now zeroed)

Co-developed-by: Frank Binns <frank.binns@imgtec.com>
Signed-off-by: Frank Binns <frank.binns@imgtec.com>
Co-developed-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Co-developed-by: Matt Coster <matt.coster@imgtec.com>
Signed-off-by: Matt Coster <matt.coster@imgtec.com>
Co-developed-by: Donald Robson <donald.robson@imgtec.com>
Signed-off-by: Donald Robson <donald.robson@imgtec.com>
Signed-off-by: Sarah Walker <sarah.walker@imgtec.com>
Reviewed-by: Faith Ekstrand <faith.ekstrand@collabora.com>