mb/hp/8460p: Add TPM support

After applying this change, /dev/tpm0 is visible inside GNU/Linux
with kernel 4.9.51-1 from Debian, and there is a menu item shown
inside SeaBIOS' (master only) interface if ESC is pressed.

The TPM is confirmed working with [Heads](https://github.com/osresearch/heads).

Change-Id: I3b845928954d203d1c3608b6704fedbd590e1fa9
Signed-off-by: Bill XIE <persmule@gmail.com>
Reviewed-on: https://review.coreboot.org/22602
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/mainboard/hp/8460p/Kconfig

@@ -29,6 +29,7 @@ config BOARD_SPECIFIC_OPTIONS # dummy
 	select SYSTEM_TYPE_LAPTOP
 	select USE_NATIVE_RAMINIT
 	select MAINBOARD_HAS_LIBGFXINIT
+	select MAINBOARD_HAS_LPC_TPM
 	select GFX_GMA_INTERNAL_IS_LVDS
 	select EC_HP_KBC1126
 	select SUPERIO_SMSC_LPC47N217

src/mainboard/hp/8460p/devicetree.cb

@@ -138,6 +138,10 @@ chip northbridge/intel/sandybridge
 					device pnp 4e.5 off #  Com2
 					end
 				end	#chip superio/smsc/lpc47n217
+
+				chip drivers/pc80/tpm
+					device pnp 0c31.0 on end
+				end
 			end
 			device pci 1f.2 on # SATA Controller 1
 				subsystemid 0x103c 0x161c