drm/nouveau: Fix suspend on some nv4x AGP cards.

On some nv4x cards (specifically, the ones that use an internal
PCIE->AGP bridge) the AGP controller state isn't preserved after a
suspend/resume cycle, and the AGP control registers have moved from
0x18xx to 0x100xx, so the FW check in nouveau_mem_reset_agp() doesn't
quite work. Check "dev->agp->mode" instead.
Signed-off-by: Francisco Jerez <currojerez@riseup.net>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_mem.c

@@ -355,7 +355,8 @@ nouveau_mem_reset_agp(struct drm_device *dev)
 	/* First of all, disable fast writes, otherwise if it's
 	 * already enabled in the AGP bridge and we disable the card's
 	 * AGP controller we might be locking ourselves out of it. */
-	if (nv_rd32(dev, NV04_PBUS_PCI_NV_19) & PCI_AGP_COMMAND_FW) {
+	if ((nv_rd32(dev, NV04_PBUS_PCI_NV_19) |
+	     dev->agp->mode) & PCI_AGP_COMMAND_FW) {
 		struct drm_agp_info info;
 		struct drm_agp_mode mode;