lenovo/x220: Enable USB 3 controller

Since only X220 with i7 have the USB3 controller this was
probably overlooked.

Before this patch lspci on Linux would not show the NEC USB 3 controller
as well as the PCI bridge it is behind. After, both the bridge and the
NEC controller can be found in the output:

    05:00.0 USB controller: NEC Corporation uPD720200 USB 3.0 Host Controller
	(rev 04)

Change-Id: I5e7e3f0c7d023f6206a7bec42a39f8955a3d9331
Signed-off-by: Marian Tietz <mtcoreboot@gmail.com>
Reviewed-on: https://review.coreboot.org/12882
Tested-by: build bot (Jenkins)
Reviewed-by: Vladimir Serbinenko <phcoder@gmail.com>

src/mainboard/lenovo/x220/devicetree.cb

@@ -109,7 +109,9 @@ chip northbridge/intel/sandybridge
 				end
 			end # PCIe Port #5 (SD)
 			device pci 1c.5 off end # PCIe Port #6
-			device pci 1c.6 off end # PCIe Port #7
+			device pci 1c.6 on
+				subsystemid 0x17aa 0x21db
+			end # PCIe Port #7
 			device pci 1c.7 off end # PCIe Port #8
 			device pci 1d.0 on
 				subsystemid 0x17aa 0x21db

src/mainboard/lenovo/x220/romstage.c

@@ -54,7 +54,7 @@ void pch_enable_lpc(void)
 void rcba_config(void)
 {
 	/* Disable unused devices (board specific) */
-	RCBA32(FD) = 0x1fe41fe3;
+	RCBA32(FD) = 0x1fa41fe3;
 	RCBA32(BUC) = 0;
 }