Convert CONFIG_SYS_LOADS_BAUD_CHANGE et al to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_LOADS_BAUD_CHANGE
   CONFIG_LOADS_ECHO

As part of this, we move CMD_SAVES to be after CMD_LOADS as they are
logically related (load or save an s-record format file) and this makes
grouping of CONFIG_SYS_LOADS_BAUD_CHANGE easier.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>