ax25-ae350: Move CONFIG_SYS_FDT_BASE to Kconfig

The address where the device tree will be passed in to U-Boot at is now
moved to the Kconfig file.  If this is user configurable, it needs to be
exposed rather than hidden, and should probably be renamed as well.

Reviewed-by: Rick Chen <rick@andestech.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/board/AndesTech/ax25-ae350/Kconfig b/board/AndesTech/ax25-ae350/Kconfig
index 91eec35..36b67f0 100644
--- a/board/AndesTech/ax25-ae350/Kconfig
+++ b/board/AndesTech/ax25-ae350/Kconfig
@@ -27,6 +27,10 @@
 config SPL_OPENSBI_LOAD_ADDR
 	default 0x01000000
 
+config SYS_FDT_BASE
+	hex
+	default 0x800f0000 if OF_SEPARATE
+
 config BOARD_SPECIFIC_OPTIONS # dummy
 	def_bool y
 	select RISCV_NDS