[U-Boot] RFC: config_distro_bootcmd aesthetic change

[Jon Nettleton]

I figured I would post this topic without the patchset I currently
have, and instead just test the waters to get some input on how the
community would feel about this change.

What I have done is to migrate all the functions from
config_distro_bootcmd.h to be .functions() so by default they are
hidden from the env print commands, but are still accessible from env
print -a.  My reasoning for doing this is as follows.

1)  It makes the more common configured environment variables the main
output of env print.  Especially on a console this makes custom
configuration far simpler to grok.
2) With another patch we can then choose the option to not store and
restore the .variables to the env instead always accepting the built
in defaults.  This makes it much simpler to upgrade the logic behind
the common distro bootflow with binary firmware updates but without
forcing a user to env default -f -a and then reset their custom
variables.
3) Reduces the storage size required for an environment on the disk.
With the two previous integration changes it reduces my saved
environment by almost 4KB.  from 4.3KB down to ~500 bytes.

I am happy to upload the patches, but again wanted to see if this is
even something that the community would even entertain integrating
before adding unnecessary patch noise.

-Jon