sh: remove undefined DEBUG preprocessor token from board config files

By default this undef is a noop, moreover at this point when the
platform support is broken is prevents debugging of U-boot by manual
insertion of #define DEBUG into common files, so it makes sense to
remove the option from all SH boards as a harmful one.

Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
Reviewed-by: Simon Glass <sjg@chromium.org>