Convert CONFIG_CMD_SPL to Kconfig

This converts the following to Kconfig:
   CONFIG_CMD_SPL

Note that trats does not actually use SPL, so this option can no-longer be
set.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index c6f5f23..43096d0 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -732,6 +732,7 @@
 	select CLK_ZYNQ
 	imply CMD_CLK
 	imply FAT_WRITE
+	imply CMD_SPL
 
 config ARCH_ZYNQMP
 	bool "Support Xilinx ZynqMP Platform"