The default shell configuration has heavy flash and memory requirements,
requiring project maintainers to set many configuration options to "n"
to keep flash and memory requirements within reason.
This adds a new configuration option, CONFIG_SHELL_MINIMAL, which will
disable flash and memory heavy options by default, and allow project
maintainers to select/imply only the options they want.
On a quick test from an ARM board I'm working on, enabling this option
cut flash space requirements by ~8 KB, and memory requirements by ~1 KB.
Signed-off-by: Jack Rosenthal <jrosenth@chromium.org>