drm/i915/dpt: pass opaque struct intel_dpt around instead of i915_address_space

drm/i915/dpt: pass opaque struct intel_dpt around instead of i915_address_space

struct i915_address_space is used in an opaque fashion in the display
parent interface, but it's just one include away from being
non-opaque. And anyway the name is rather specific.

Switch to using the struct intel_dpt instead, which embeds struct
i915_address_space anyway. With the definition hidden in i915_dpt.c,
this can't be accidentally made non-opaque, and the type seems rather
more generic anyway.

We do have to add a new helper i915_dpt_to_vm(), as there's one case in
intel_fb_pin_to_dpt() that requires direct access to struct
i915_address_space. But this just underlines the point about opacity.

Reviewed-by: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>
Link: https://patch.msgid.link/daa39178c0b0305b010564952d691f06e3cd63ca.1772030909.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>