sunxi: introduce extra config option for boot0 header

The ENABLE_ARM_SOC_BOOT0_HOOK option is a generic option shared with
other boards. To allow alternative code to be inserted, we create
another, now function specific config symbol on top of it to simplify
later additions. No functional change at this time.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Jagan Teki <jagan@openedev.com>

board/sunxi/Kconfig

@@ -133,6 +133,15 @@ config MACH_SUN8I
 	bool
 	default y if MACH_SUN8I_A23 || MACH_SUN8I_A33 || MACH_SUN8I_H3 || MACH_SUN8I_A83T
 
+config RESERVE_ALLWINNER_BOOT0_HEADER
+	bool "reserve space for Allwinner boot0 header"
+	select ENABLE_ARM_SOC_BOOT0_HOOK
+	---help---
+	Prepend a 1536 byte (empty) header to the U-Boot image file, to be
+	filled with magic values post build. The Allwinner provided boot0
+	blob relies on this information to load and execute U-Boot.
+	Only needed on 64-bit Allwinner boards so far when using boot0.
+
 config DRAM_TYPE
 	int "sunxi dram type"
 	depends on MACH_SUN8I_A83T

configs/pine64_plus_defconfig

@@ -1,5 +1,5 @@
 CONFIG_ARM=y
-CONFIG_ENABLE_ARM_SOC_BOOT0_HOOK=y
+CONFIG_RESERVE_ALLWINNER_BOOT0_HEADER=y
 CONFIG_ARCH_SUNXI=y
 CONFIG_MACH_SUN50I=y
 CONFIG_DRAM_CLK=672