riscv: mbv: Switch to OF_SEPARATE with fixed address

Hardcode DTB address to specific address.

Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/a5ad3c8d21be311254dd950e4e322d13cacdc176.1707911544.git.michal.simek@amd.com
diff --git a/board/xilinx/Kconfig b/board/xilinx/Kconfig
index 843198f..5c4ad8f 100644
--- a/board/xilinx/Kconfig
+++ b/board/xilinx/Kconfig
@@ -45,6 +45,7 @@
 	default 0x1000 if ARCH_VERSAL || ARCH_VERSAL_NET
 	default 0x8000 if MICROBLAZE
 	default 0x100000 if ARCH_ZYNQ || ARCH_ZYNQMP
+	default 0x23000000 if TARGET_XILINX_MBV
 	depends on OF_BOARD || OF_SEPARATE
 	help
 	  Offset in the memory where the board configuration DTB is placed.