rockchip: add option to change method of loading u-boot

If we would like to boot from SD card, we have to implement mmc driver
in SPL stage, and get a slightly large SPL binary. Rockchip SoC's
bootrom code has the ability to load spl and u-boot, then boot.

If CONFIG_ROCKCHIP_SPL_BACK_TO_BROM is enabled, the spl will return to
bootrom in board_init_f(), then bootrom loads u-boot binary.

Loading sequence after rework:
bootrom ==> spl ==> bootrom ==> u-boot

Signed-off-by: Ziyuan Xu <xzy.xu@rock-chips.com>
Acked-by: Simon Glass <sjg@chromium.org>
Fixed up spelling of U-Boot, boorom, opinion->option, Rochchip:
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/mach-rockchip/Kconfig b/arch/arm/mach-rockchip/Kconfig
index c49cc19..cf718fa 100644
--- a/arch/arm/mach-rockchip/Kconfig
+++ b/arch/arm/mach-rockchip/Kconfig
@@ -17,6 +17,14 @@
 	  and video codec support. Peripherals include Gigabit Ethernet,
 	  USB2 host and OTG, SDIO, I2S, UART, SPI, I2C and PWMs.
 
+config ROCKCHIP_SPL_BACK_TO_BROM
+	bool "SPL returns to bootrom"
+	default y if ROCKCHIP_RK3036
+	help
+	  Rockchip SoCs have ability to load SPL & U-Boot binary. If enabled,
+          SPL will return to the boot rom, which will then load the U-Boot
+          binary to keep going on.
+
 source "arch/arm/mach-rockchip/rk3288/Kconfig"
 source "arch/arm/mach-rockchip/rk3036/Kconfig"
 endif