rockchip: rk3588-nanopc-t6: Build SPI image

Enable building of the SPI image, u-boot-rockchip-spi.bin, now that we
know what bootsource id values BootRom use for SPI flash on RK3588.

Fixes: b0b8086898f8 ("board: rockchip: add FriendlyElec NanoPC-T6 rk3588 board")
Signed-off-by: John Clark <inindev@gmail.com>
Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/configs/nanopc-t6-rk3588_defconfig b/configs/nanopc-t6-rk3588_defconfig
index 62f307a..7609932 100644
--- a/configs/nanopc-t6-rk3588_defconfig
+++ b/configs/nanopc-t6-rk3588_defconfig
@@ -14,6 +14,7 @@
 CONFIG_DEFAULT_DEVICE_TREE="rk3588-nanopc-t6"
 CONFIG_ROCKCHIP_RK3588=y
 CONFIG_SPL_ROCKCHIP_COMMON_BOARD=y
+CONFIG_ROCKCHIP_SPI_IMAGE=y
 CONFIG_SPL_SERIAL=y
 CONFIG_SPL_STACK_R_ADDR=0x600000
 CONFIG_TARGET_NANOPCT6_RK3588=y