ARM64: zynqmp: Force certain bootmode for SPL

ZynqMP provides an option to overwrite bootmode setting which
can change SPL behavior.
For example: boot SPL via JTAG and then SPL loads images from SD.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>

arch/arm/cpu/armv8/zynqmp/Kconfig

@@ -74,7 +74,7 @@ config SPL_ZYNQMP_ALT_BOOTMODE
 
 choice
 	prompt "Boot mode"
-	depends on ZYNQMP_ALT_BOOTMODE_ENABLED
+	depends on SPL_ZYNQMP_ALT_BOOTMODE_ENABLED
 	default JTAG
 
 config JTAG_MODE