rk3288: spl: Add dram_init_banksize

Falcon mode, is updating DDR dt node configuration through
spl_fixup_fdt() so add appropriate DDR base and size through
dram_init_banksize.

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