baytrail: allow function disable on TXE

Previously it was not known how to put the TXE pci device
into D3Hot. It's been disseminated that this is not a requirement
for disabling the TXE pci device in the function disable register.
Therefore, allow this by returning 0 from place_device_in_d3hot().

BUG=chrome-os-partner:22871
BRANCH=None
TEST=Temporarily set TXE to be disabled. Noted FUNC_DIS was being
     set accordingly.

Change-Id: Ibf537bf8ba718859591dc89bdf41e57c1ea9d836
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/175490
Reviewed-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: http://review.coreboot.org/4925
Tested-by: build bot (Jenkins)
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

src/soc/intel/baytrail/southcluster.c

@@ -322,7 +322,8 @@ static int place_device_in_d3hot(device_t dev)
 		offset = 0x50;
 		break;
 	case PCI_DEVFN(TXE_DEV, TXE_FUNC):
-		break;
+		/* TXE cannot be placed in D3Hot. */
+		return 0;
 	case PCI_DEVFN(PCIE_PORT1_DEV, PCIE_PORT1_FUNC):
 		offset = 0xa0;
 		break;