board: ti: Define Kconfig symbol for common cmd options

Instead of defining command options in every defconfig,
define a common Kconfig symbol that consolidates all command
options that are supported by any TI platform. Also use imply
keyword so that that specific option can be disabled if
not required.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>