fdt: Enable OF_HAS_PRIOR_STAGE for most boards with OF_BOARD

Use this new Kconfig instead of OF_BOARD, so we know for sure which boards
obtain their devicetree from a prior stage. Leave sandbox alone since it
does not. Also don't touch xilinx_versal_virt since it does not have a
specific TARGET Kconfig.

This option implies OF_BOARD for now, but with future work standard
passage may be used instead.

Signed-off-by: Simon Glass <sjg@chromium.org>
[trini: Add rpi_4_32b and rpi_arm64 to the list of boards converted]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/arch/powerpc/cpu/mpc85xx/Kconfig b/arch/powerpc/cpu/mpc85xx/Kconfig
index 836aedd..d71ca86 100644
--- a/arch/powerpc/cpu/mpc85xx/Kconfig
+++ b/arch/powerpc/cpu/mpc85xx/Kconfig
@@ -109,6 +109,7 @@
 	bool "Support qemu-ppce500"
 	select ARCH_QEMU_E500
 	select PHYS_64BIT
+	imply OF_HAS_PRIOR_STAGE
 
 config TARGET_T1024RDB
 	bool "Support T1024RDB"