mb/emulation/qemu-q35: Enable option for TPM

This enables the mainboard to use a TPM if it is selected in the
configuration.  By default this does nothing, but it allows the
TPM to be enabled and used with the CONFIG_USER_TPM2 Kconfig option.

Using a TPM with QEMU requires either a physical TPM backend or
the swtpm package with a socket:

  -chardev socket,id=swtpm,path=/tmp/swtpm/socket
  -tpmdev emulator,id=tpm0,chardev=swtpm
  -device tpm-tis,tpmdev=tpm0

Change-Id: I0d79a5a0f590c57998ababb660b52d9e3ed2d484
Signed-off-by: Duncan Laurie <dlaurie@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/39836
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

src/mainboard/emulation/qemu-q35/Kconfig

@@ -12,6 +12,7 @@ config BOARD_SPECIFIC_OPTIONS
 	select BOARD_ROMSIZE_KB_16384 if VBOOT
 	select MAINBOARD_HAS_NATIVE_VGA_INIT
 	select MAINBOARD_FORCE_NATIVE_VGA_INIT
+	select MAINBOARD_HAS_LPC_TPM
 
 config VBOOT
 	select VBOOT_MUST_REQUEST_DISPLAY

src/mainboard/emulation/qemu-q35/devicetree.cb

@@ -8,7 +8,11 @@ chip mainboard/emulation/qemu-q35
 		device pci 0.0 mandatory end		# northbridge (q35)
 		chip southbridge/intel/i82801ix
 			# present unconditionally
-			device pci 1f.0 mandatory end	# LPC
+			device pci 1f.0 mandatory
+				chip drivers/pc80/tpm
+					device pnp 0c31.0 on end
+				end
+			end	# LPC
 			device pci 1f.2 on end	# SATA
 			device pci 1f.3 on end	# SMBus