board: xilinx: Enable changing default DTB pick up address

U-Boot on xilinx boards is checking one address where DTB can be placed as
the first location for DTB. Originally this code was developed for Versal
where QEMU was putting generated DTB for U-Boot to use.
The patch enables changing this address which is necessary for cases where
default address is pointing to location (DDR) which is not present. The
access to this location can cause exception.

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

board/xilinx/Kconfig

@@ -41,7 +41,7 @@ config XILINX_PS_INIT_FILE
 endif
 
 config XILINX_OF_BOARD_DTB_ADDR
-	hex
+	hex "Default DTB pickup address"
 	default 0x1000 if ARCH_VERSAL
 	default 0x100000 if ARCH_ZYNQ || ARCH_ZYNQMP
 	depends on OF_BOARD || OF_SEPARATE