mb/google/kahlee/variants/grunt: Enable BayHub720 driver

Enable this driver along with power saving.

BUG=b:73726008
BRANCH=none
TEST=boot and see this message:
BayHub BH720: Power-saving enabled 110103
From linux:
$ iotools pci_read32 2 0 0 0x90
0x00110103

Change-Id: I850e923f73e01fe629d66ad61b65afa58035845c
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-on: https://review.coreboot.org/25967
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
diff --git a/src/mainboard/google/kahlee/Kconfig b/src/mainboard/google/kahlee/Kconfig
index 22925f4..24881b5 100644
--- a/src/mainboard/google/kahlee/Kconfig
+++ b/src/mainboard/google/kahlee/Kconfig
@@ -36,6 +36,7 @@
 	select SOC_AMD_PSP_SELECTABLE_SMU_FW
 	select SOC_AMD_SMU_FANLESS
 	select HAVE_ACPI_RESUME
+	select DRIVERS_GENERIC_BH720 if BOARD_GOOGLE_GRUNT
 
 if BOARD_GOOGLE_BASEBOARD_KAHLEE
 
diff --git a/src/mainboard/google/kahlee/variants/grunt/devicetree.cb b/src/mainboard/google/kahlee/variants/grunt/devicetree.cb
index cfc3198..151d902 100644
--- a/src/mainboard/google/kahlee/variants/grunt/devicetree.cb
+++ b/src/mainboard/google/kahlee/variants/grunt/devicetree.cb
@@ -62,7 +62,12 @@
 		device pci 2.1 on  end #
 		device pci 2.2 on  end #
 		device pci 2.3 on  end #
-		device pci 2.4 on  end #
+		device pci 2.4 on
+			chip drivers/generic/bayhub
+				register "power_saving" = "1"
+				device pci 00.0 on end
+			end
+		end #
 		device pci 2.5 on  end #
 		device pci 8.0 on  end # PSP
 		device pci 9.0 on  end # PCIe Host Bridge