kconfig: move CONFIG_CMD_GO to Kconfig

Since CONFIG_CMD_GO is defined in config_cmd_defaults.h
(and no board undefs it its own header), it can be moved to
Kconfig with the default value "y".

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Acked-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>