tegra: add Colibri T20 board support

This adds board support for the Toradex Colibri T20 module.

Working functions:
- SD card boot
- USB boot
- Network
- NAND environment

Signed-off-by: Lucas Stach <dev@lynxeye.de>
Signed-off-by: Tom Warren <twarren@nvidia.com>
diff --git a/boards.cfg b/boards.cfg
index 4c63789..c45556e 100644
--- a/boards.cfg
+++ b/boards.cfg
@@ -278,6 +278,7 @@
 seaboard                     arm         armv7:arm720t seaboard          nvidia         tegra20
 ventana                      arm         armv7:arm720t ventana           nvidia         tegra20
 whistler                     arm         armv7:arm720t whistler          nvidia         tegra20
+colibri_t20_iris             arm         armv7:arm720t colibri_t20_iris  toradex        tegra20
 u8500_href                   arm         armv7       u8500               st-ericsson    u8500
 snowball                     arm         armv7       snowball               st-ericsson    u8500
 kzm9g                        arm         armv7       kzm9g               kmc            rmobile