drm/i915/debugfs: register LPSP capability on all platforms

The debugfs file shows it's not capable, don't duplicate the info.

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/939453050a5a5175a12a08f16542c1b40bd726dc.1630327990.git.jani.nikula@intel.com