include/configs: remove CONFIG_SYS_CBSIZE when the default value is used

Now that include/config_fallbacks.h define a sane fallback for
CONFIG_SYS_CBSIZE, we can drop the definition of this constant in all
configurations that were using the default value.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
[trini: Drop <config.h> from stih410-b2260.h]
Signed-off-by: Tom Rini <trini@konsulko.com>