mb/facebook/watson/v2: enable IPMI to be detected as PNP device

Watson v2 mainboard has hardware support and OpenBMC support for IPMI.

Add drivers/ipmi to the device tree of watson v2 mainboard.

Use original device tree for watson mainboard.

TESTED=booted watson v2 board, and tested ipmitool command:
   0 | OEM record fb | 2800000000f0ffffffffffffff

Signed-off-by: Ravi Rama <rrama@arista.com>
Signed-off-by: Jonathan Zhang <jonzhang@fb.com>
Change-Id: I1be653278dbfd704d24756cf82be73bdae4bb13c
Reviewed-on: https://review.coreboot.org/c/coreboot/+/51311
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Christian Walter <christian.walter@9elements.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/facebook/watson/Kconfig

@@ -37,6 +37,10 @@ config MAINBOARD_PART_NUMBER
 	string
 	default "Watson"
 
+config DEVICETREE
+	string
+	default "variants/$(CONFIG_VARIANT_DIR)/devicetree.cb"
+
 config IRQ_SLOT_COUNT
 	int
 	default 18
@@ -47,6 +51,7 @@ config CBFS_SIZE
 
 config VARIANT_DIR
 	string
+	default "watson" if BOARD_FACEBOOK_WATSON
 	default "watson_v2" if BOARD_FACEBOOK_WATSON_V2
 
 config VBOOT_FWID_MODEL

src/mainboard/facebook/watson/variants/watson_v2/devicetree.cb

@@ -0,0 +1,23 @@
+chip soc/intel/fsp_broadwell_de
+	device cpu_cluster 0 on
+		device lapic 0 on end
+	end
+	device domain 0 on
+		device pci 00.0 on end # SoC router
+		device pci 14.0 on end # xHCI Controller
+		device pci 19.0 on end # Gigabit LAN Controller
+		device pci 1d.0 on end # EHCI Controller
+		device pci 1f.0 on # LPC Bridge
+			chip drivers/pc80/tpm
+				device pnp 0c31.0 on end
+			end
+			chip drivers/ipmi
+				device pnp ca2.0 on end
+				register "bmc_i2c_address" = "0x20"
+			end
+		end
+		device pci 1f.2 on end # SATA Controller
+		device pci 1f.3 on end # SMBus Controller
+		device pci 1f.5 on end # SATA Controller
+	end
+end