PCIe: Add L1 Sub-State support.

Enable L1 Sub-State when both root port and endpoint support it.

[pg: keyed the feature to MMCONF_SUPPORT, otherwise boards
without that capability fail to build.]

Change-Id: Id11fc7c73eb865411747eef63f5f901e00a17f84
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: 6ac04ad7e2261846e40da297f7fa317ccebda092
Original-BUG=chrome-os-partner:31424
Original-TEST=Build a image and run on Samus proto boards to check if the
settings are applied correctly. I just only have proto boards and
need someone having EVT boards to confirm the settings.
Original-Signed-off-by: Kenji Chen <kenji.chen@intel.com>
Original-Change-Id: Id1b5a52ff0b896f4531c4a6e68e70a2cea8c736a
Original-Reviewed-on: https://chromium-review.googlesource.com/221436
Original-Reviewed-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: http://review.coreboot.org/8832
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
diff --git a/src/device/Kconfig b/src/device/Kconfig
index 7f43888..8ddb58c 100644
--- a/src/device/Kconfig
+++ b/src/device/Kconfig
@@ -271,6 +271,14 @@
 	  This option enables static configuration for a single pre-defined
 	  PCI bridge function on bus 0.
 
+config PCIEXP_L1_SUB_STATE
+	prompt "Enable PCIe ASPM L1 SubState"
+	bool
+	depends on PCIEXP_PLUGIN_SUPPORT && MMCONF_SUPPORT
+	default n
+	help
+	  Detect and enable ASPM on PCIe links.
+
 if EARLY_PCI_BRIDGE
 
 config EARLY_PCI_BRIDGE_DEVICE