sunxi: SPL SPI: Add SPI boot support for the Allwinner R40 SoC

Now that we can easily select an SoC specific SPI0 base address, adding
support for the Allwinner R40 is fairly trivial:
We set the base address, add this SoC to the ones that use PC23 and
enable it in Kconfig.

This allows booting from SPI flash on R40 boards.

Tested on a Bananapi M2 Berry with SPI flash connected to the header pins.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>
diff --git a/arch/arm/mach-sunxi/Kconfig b/arch/arm/mach-sunxi/Kconfig
index 3a3b673..eb04616 100644
--- a/arch/arm/mach-sunxi/Kconfig
+++ b/arch/arm/mach-sunxi/Kconfig
@@ -994,7 +994,7 @@
 
 config SPL_SPI_SUNXI
 	bool "Support for SPI Flash on Allwinner SoCs in SPL"
-	depends on MACH_SUN4I || MACH_SUN5I || MACH_SUN7I || MACH_SUNXI_H3_H5 || MACH_SUN50I
+	depends on MACH_SUN4I || MACH_SUN5I || MACH_SUN7I || MACH_SUNXI_H3_H5 || MACH_SUN50I || MACH_SUN8I_R40
 	help
 	  Enable support for SPI Flash. This option allows SPL to read from
 	  sunxi SPI Flash. It uses the same method as the boot ROM, so does