soc/intel/skylake: Add PcieRpClkSrcNumber UPD configuartion support

New UPD PcieRpClkSrcNumber introduced in FSP V2.9.2 to configure
clock source number of PCIe root ports. This UPD array is set to clock
source number(0-6) for all the enabled PCIe root ports, invalid(0x1F)
is set for disabled PCIe root ports.

BUG=b:70252901
BRANCH=None
TEST= Perform the following
1. Build and boot soraka
2. Verify PCIe devices list using lspci command
3. Perform Basic Assurance Test(BAT) on soraka

Change-Id: I95ca0d893338100b7e4d7d0b76c076ed7e2b040e
Signed-off-by: Divya Chellap <divya.chellappa@intel.com>
Reviewed-on: https://review.coreboot.org/22947
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Subrata Banik <subrata.banik@intel.com>
Reviewed-by: Furquan Shaikh <furquan@google.com>
diff --git a/src/mainboard/google/poppy/variants/soraka/devicetree.cb b/src/mainboard/google/poppy/variants/soraka/devicetree.cb
index 22349d6..3bcda3c 100644
--- a/src/mainboard/google/poppy/variants/soraka/devicetree.cb
+++ b/src/mainboard/google/poppy/variants/soraka/devicetree.cb
@@ -156,6 +156,8 @@
 	register "PcieRpAdvancedErrorReporting[0]" = "1"
 	# RP 1, Enable Latency Tolerance Reporting Mechanism
 	register "PcieRpLtrEnable[0]" = "1"
+	# RP 1 uses uses CLK SRC 1
+	register "PcieRpClkSrcNumber[0]" = "1"
 
 	register "usb2_ports[0]" = "USB2_PORT_LONG(OC0)"	# Type-C Port 1
 	register "usb2_ports[1]" = "USB2_PORT_MID(OC_SKIP)"	# Type-A Port