mb/asrock/h110m: disable CLKREQ to use onboard LAN

The PCH uses the SRCCLKREQ# pin to detect PCIe device in the slot in
order to send clock signal to it. However, this logic is not required
for the Realtek LAN device, since this chip is soldered to the board
and always uses clocking. The chipset can't receive the clock request
signal (most likely this pin isn't connected) and doesn't enable the
CLK. For this reason, the device is broken during the initialization
phase. The patch disables clock request logic for the PCH PCIe port 6
to initialize the onboard LAN device correctly.

Change-Id: I5cbce6177c89052eb50959f43903b6f8a607e77f
Signed-off-by: Maxim Polyakov <max.senia.poliak@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/36377
Reviewed-by: Patrick Rudolph <siro@das-labor.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/asrock/h110m/devicetree.cb

@@ -219,10 +219,8 @@ chip soc/intel/skylake
 
 	# Enable Root port 6(x1) for LAN.
 	register "PcieRpEnable[5]" = "1"
-	# Enable CLKREQ#
-	register "PcieRpClkReqSupport[5]" = "1"
-	# Use SRCCLKREQ1#
-	register "PcieRpClkReqNumber[5]" = "1"
+	# Disable CLKREQ#, since onboard LAN is always present
+	register "PcieRpClkReqSupport[5]" = "0"
 	# Enable Advanced Error Reporting
 	register "PcieRpAdvancedErrorReporting[5]" = "1"
 	# Enable Latency Tolerance Reporting Mechanism