mainboard/google/kahlee: Enable ASPM on PCI express

We should use active-state power management where possible to reduce
power consumption during normal operation. Enable these options.

Linux does not seem to enable this for AMD, and the Intel code in coreboot
does enable these options.

PCIEXP_COMMON_CLOCK is enabled also, to follow how Intel does it.

BUG=b:110041917
TEST=boot on grunt, see that WiFi and eMMC still run OK

Change-Id: Ia7c711304ffe460a9fb0d4f654a51485958239ea
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-on: https://review.coreboot.org/27464
Reviewed-by: Martin Roth <martinroth@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/google/kahlee/Kconfig

@@ -39,6 +39,10 @@ config BOARD_GOOGLE_BASEBOARD_KAHLEE
 	select DRIVERS_GENERIC_ADAU7002
 	select DRIVERS_GENERIC_MAX98357A
 	select DRIVERS_I2C_DA7219
+	select PCIEXP_ASPM
+	select PCIEXP_CLK_PM
+	select PCIEXP_COMMON_CLOCK
+	select PCIEXP_L1_SUB_STATE
 	select HAVE_EM100_SUPPORT
 
 if BOARD_GOOGLE_BASEBOARD_KAHLEE