sunxi: Kconfig: introduce SUNXI_MINIMUM_DRAM_MB

Traditionally we assumed that every Allwinner board would come with at
least 256 MB of DRAM, and set our DRAM layout accordingly. This affected
both the default load addresses, but also U-Boot's own address
expectations (like being loaded at 160 MB).

Some SoCs come with co-packaged DRAM, but only provide 32 or 64MB. So
far we special-cased those *chips*, as there was only one chip per DRAM
size. However new chips force us to take a more general approach.

Introduce a Kconfig symbol, which provides the minimum DRAM size of the
board. If nothing else is specified, we use 256 MB, and default to
smaller values for those co-packaged SoCs.
Then select the different DRAM maps according to this new symbol, so
that different SoCs with the same DRAM size can share those definitions.

Inspired by an idea from Icenowy.

This is just refactoring: compiled for all boards before and after this
patch: the binaries were identical.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Jernej Skrabec <jernej.skrabec@gmail.com>

arch/arm/mach-sunxi/Kconfig

@@ -615,6 +615,18 @@ config SYS_BOARD
 config SYS_SOC
 	default "sunxi"
 
+config SUNXI_MINIMUM_DRAM_MB
+	int "minimum DRAM size"
+	default 32 if MACH_SUNIV
+	default 64 if MACH_SUN8I_V3S
+	default 256
+	---help---
+	Minimum DRAM size expected on the board. Traditionally we assumed
+	256 MB, so that U-Boot would load at 160MB. With co-packaged DRAM
+	we have smaller sizes, though, so that U-Boot's own load address and
+	the default payload addresses must be shifted down.
+	This is expected to be fixed by the SoC selection.
+
 config UART0_PORT_F
 	bool "UART0 on MicroSD breakout board"
 	---help---