rockchip: fixup board choice in Kconfig

Kconfig for board target select is choice option, fixup for
rk3036, rk3288 and rv1108.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/arch/arm/mach-rockchip/rk3288/Kconfig b/arch/arm/mach-rockchip/rk3288/Kconfig
index c5dcd06..a32cd92 100644
--- a/arch/arm/mach-rockchip/rk3288/Kconfig
+++ b/arch/arm/mach-rockchip/rk3288/Kconfig
@@ -1,5 +1,8 @@
 if ROCKCHIP_RK3288
 
+choice
+	prompt "RK3288 board select"
+
 config TARGET_CHROMEBOOK_JERRY
 	bool "Google/Rockchip Veyron-Jerry Chromebook"
 	select BOARD_LATE_INIT
@@ -125,6 +128,8 @@
 	  8GB eMMC and 2GB of SDRAM. Expansion connectors provide access to
 	  I2C, SPI, UART, GPIOs.
 
+endchoice
+
 config ROCKCHIP_FAST_SPL
 	bool "Change the CPU to full speed in SPL"
 	depends on TARGET_CHROMEBOOK_JERRY