rockchip: puma-rk3399: migrate to u-boot-rockchip-spi.bin

Now that a single binary containing TPL/SPL correctly formatted for SPI
flashes and U-Boot proper, can be generated by binman, let's do it.

Also update the documentation to tell the user to use this newly
generated file instead of manually generating and flashing the binaries.

Cc: Quentin Schulz <foss+uboot@0leil.net>
Signed-off-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/configs/puma-rk3399_defconfig b/configs/puma-rk3399_defconfig
index 50d7591..34186d1 100644
--- a/configs/puma-rk3399_defconfig
+++ b/configs/puma-rk3399_defconfig
@@ -9,6 +9,7 @@
 CONFIG_DEFAULT_DEVICE_TREE="rk3399-puma-haikou"
 CONFIG_ROCKCHIP_RK3399=y
 CONFIG_ROCKCHIP_BOOT_MODE_REG=0x0
+CONFIG_ROCKCHIP_SPI_IMAGE=y
 CONFIG_TARGET_PUMA_RK3399=y
 CONFIG_DEBUG_UART_BASE=0xFF180000
 CONFIG_DEBUG_UART_CLOCK=24000000