[U-Boot] Automatic software updates in U-Boot

Hello,

This patch series adds support for automatic software updates from a TFTP server. First patch introduces some changes in the TFTP timeout handling that are required by the feature proper, which is contained in the second patch. Third patch provides minor enhancements to the iminfo output that can become handy when using the new feature.

Please see newly added doc/README.au_tftp for more details.

Code has been compile-tested on several ppc, arm and mips targets. The feature itself has been tested on TQM8555 and MPC8555CDS.

Regards, Bartlomiej Sieka