Fix number base handling of "load" command

As documented, almost all U-Boot commands expect numbers to be entered
in hexadecimal input format. (Exception: for historical reasons, the
"sleep" command takes its argument in decimal input format.)

This rule was broken for the "load" command; for details please see
especially commits 045fa1e1 "fs: add filesystem switch libary,
implement ls and fsload commands" and 3f83c87e "fs: fix number base
behaviour change in fatload/ext*load".  In the result, the load
command would always require an explicit "0x" prefix for regular
(i. e. base 16 formatted) input.

Change this to use the standard notation of base 16 input format.
While strictly speaking this is a change of the user interface, we
hope that it will not cause trouble.  Stephen Warren comments (see
[1]):

        I suppose you can change the behaviour if you want; anyone
        writing "0x..." for their values presumably won't be
        affected, and if people really do assume all values in U-Boot
        are in hex, presumably nobody currently relies upon using
        non-prefixed values with the generic load command, since it
        doesn't work like that right now.

[1] http://article.gmane.org/gmane.comp.boot-loaders.u-boot/171172



Acked-by: Tom Rini <trini@ti.com>
Acked-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Wolfgang Denk <wd@denx.de>