drm/i915/debugfs: move IPS debugfs to hsw_ips.c

Follow the style of placing debugfs next to the implementation.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230302161617.2978821-1-jani.nikula@intel.com