drm/i915/debugfs: move PCH type to display caps

Arguably PCH is more relevant to display. Move the information to
display caps debugfs.

Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Link: https://lore.kernel.org/r/a864b7a577ea7a3bd2435e9734e023593edbfd5a.1744295009.git.jani.nikula@intel.com


Signed-off-by: Jani Nikula <jani.nikula@intel.com>