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>
diff --git a/arch/arm/mach-rockchip/rk3288/Kconfig b/arch/arm/mach-rockchip/rk3288/Kconfig
index 94863a9..c53d2e2 100644
--- a/arch/arm/mach-rockchip/rk3288/Kconfig
+++ b/arch/arm/mach-rockchip/rk3288/Kconfig
@@ -81,9 +81,6 @@
 config SPL_LIBGENERIC_SUPPORT
 	default y
 
-config SPL_MMC_SUPPORT
-	default y
-
 config SPL_SERIAL_SUPPORT
 	default y