sconfig: Add a new mmio resource type

Add support for a mmio resource in the devicetree to allow
memory-mapped IO addresses to be assigned to given values.

AMD platforms perform a significant amount of configuration through
these MMIO addresses, including I2C bus configuration.

BUG=b:72121803

Change-Id: I5608721c22c1b229f527815b5f17fff3a080c3c8
Signed-off-by: Justin TerAvest <teravest@chromium.org>
Reviewed-on: https://review.coreboot.org/23319
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>

util/showdevicetree/showdt.c

@@ -91,6 +91,9 @@ const char *dev_path(device_t dev)
 		case DEVICE_PATH_CPU_BUS:
 			sprintf(buffer, "CPU_BUS: %02x", dev->path.cpu_bus.id);
 			break;
+		case DEVICE_PATH_MMIO:
+			sprintf(buffer, "MMIO: %08x", dev->path.mmio.addr);
+			break;
 		default:
 			printf("Unknown device path type: %d\n",
 			       dev->path.type);