rockchip: Convert to use FIT generator for optee

Use generator script so that we can use environment for TEE source.
$TEE for tee.bin, and if file not exist, the script can report a warning,
and meke the build success without a error.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/configs/evb-rk3229_defconfig b/configs/evb-rk3229_defconfig
index 745fdd1..11a2d01 100644
--- a/configs/evb-rk3229_defconfig
+++ b/configs/evb-rk3229_defconfig
@@ -14,7 +14,7 @@
 CONFIG_FIT=y
 CONFIG_FIT_VERBOSE=y
 CONFIG_SPL_LOAD_FIT=y
-CONFIG_SPL_FIT_SOURCE="arch/arm/mach-rockchip/fit_spl_optee.its"
+CONFIG_SPL_FIT_GENERATOR="arch/arm/mach-rockchip/fit_spl_optee.sh"
 CONFIG_USE_PREBOOT=y
 CONFIG_DEFAULT_FDT_FILE="rk3229-evb.dtb"
 # CONFIG_DISPLAY_CPUINFO is not set