secure_boot: include/configs: move definition of CONFIG_CMD_BLOB

CONFIG_CMD_BLOB must be defined in case of Secure Boot. It was
earlier defined in all config files. The definition has been
moved to a common file which is included by all configs.

Signed-off-by: Aneesh Bansal <aneesh.bansal@nxp.com>
Acked-by: Ruchika Gupta <ruchika.gupta@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>