[U-Boot] common/cmd_disk.c doesn't actually define any "commands"

[Robert P. J. Day]

   i know i mentioned it this weekend but the only reason i tripped
over that cmd_disk.c thingie is that i built myself a cmd_*.c
reference list, matching source files with defined commands and
any preprocessor conditions that defined them here:

http://www.crashcourse.ca/wiki/index.php/U-Boot_command/file_reference

   i just wanted a truly up-to-date list of u-boot commands, where
they come from, and any CONFIG_ settings necessary for compiling them
into the u-boot image.  it was, unsurprisingly, a very educational
experience, where i wandered across the occasional oddity.

rday