rk3288: vyasa: Add eMMC boot support

RK3288 Vyasa has eMMC boot support, with JP4 open.

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>