uboot-imx

rk3288: kconfig: remove duplicate definition of SPL_MMC_SUPPORT

SPL_MMC_SUPPORT defined in rockchip top level Kconfig instead of
inside rk3288 and default to disable if ROCKCHIP_SPL_BACK_TO_BROM
defined.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Reviewed-by: Simon Glass <sjg@chromium.org>