[U-Boot] Automatic software updates in U-Boot -- version 2

[Bartlomiej Sieka]

Hello,

This is the second version of the patch series adding support for automatic
software updates from a TFTP server. V2 adds millisecond granularity of the
TFTP timeouts and addresses comments posted to the ML for the first version.

First three patches make some general changes required by the new feature,
first one in the Flash subsystem, second and third in the networking code.
Then follows a minor clean-up, with the feature proper in fifth patch. Last
patch provides minor enhancements to the iminfo output that can become handy
when using the new feature.

Please see newly added doc/README.update 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 and trab boards.

Note that the second patch might introduce networking issues for boards not
conforming to the following two mandatory requirements:
- CFG_HZ should be set to 1000
- get_timer() should return milliseconds

An example of such a non-conformant board is the trab, which when run with
the networking changes mentioned above indeed exhibits timeouts during TFTP
transfers. Also, the default timeouts of the auto-update feature have to be
significantly increased for the trab target (CONFIG_UPDATE_TFTP_MSEC_MAX set
to 1000000, instead of the default 100).

Regards,
Bartlomiej Sieka