Enable L1 Sub-State when both root port and endpoint support it.
BUG=chrome-os-partner:31424
TEST=Build a image and run on Samus proto boards to check if the
settings are applied correctly. I just only have proto boars and
need someone having EVT boards to confirm the settings.
Signed-off-by: Kenji Chen <kenji.chen@intel.com>
Change-Id: Id1b5a52ff0b896f4531c4a6e68e70a2cea8c736a
Reviewed-on: https://chromium-review.googlesource.com/221436
Reviewed-by: Duncan Laurie <dlaurie@chromium.org>