ARM: dts: renesas: Reserve space in 64bit R-Car DTs

Reserve 4 kiB of space in 64bit R-Car DTs when those DTs are compiled
to permit patching in OpTee-OS /firmware node, /reserved-memory node,
possibly also additional /memory@ nodes and RPC node by TFA.

This duplicates behavior in arch/arm/dts/Makefile with OF_UPSTREAM.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Reviewed-by: Sumit Garg <sumit.garg@linaro.org>

dts/upstream/src/arm64/Makefile

@@ -7,6 +7,10 @@ targets += $(dtb-y)
 # Add any required device tree compiler flags here
 DTC_FLAGS += -a 0x8
 
+ifdef CONFIG_RCAR_64
+DTC_FLAGS += -R 4 -p 0x1000
+endif
+
 PHONY += dtbs
 dtbs: $(addprefix $(obj)/, $(dtb-y))
 	@: