dm: rockchip: Enable CONFIG_BLK

Enable CONFIG_BLK to move to using driver model for block devices. This
affects MMC booting in SPL, as well as MMC access in U-Boot proper.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/mach-rockchip/Kconfig b/arch/arm/mach-rockchip/Kconfig
index d3bddb7..2a8afac 100644
--- a/arch/arm/mach-rockchip/Kconfig
+++ b/arch/arm/mach-rockchip/Kconfig
@@ -41,6 +41,9 @@
 config DM_GPIO
 	default y
 
+config BLK
+	default y
+
 source "arch/arm/mach-rockchip/rk3288/Kconfig"
 source "arch/arm/mach-rockchip/rk3036/Kconfig"
 endif