SPL: SPI: select SPL_SPI_FLASH_SUPPORT on SPL_SPI_SUNXI

The Allwinner SPI flash SPL boot support is guarded by the SPL_SPI_SUNXI
symbol. But despite its generic name, the actual only use case for this
is to provide SPI flash support to the SPL, which requires
CONFIG_SPL_SPI_FLASH_SUPPORT to be defined.
Select this symbol from the SPL_SPI_SUNXI Kconfig definition. This
avoids doing this explicitly in the defconfig, and fixes SPI booting on
the Pine64 SoPine (and -LTS version) and the OrangePi Win board (both with
SPI flash).

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>

configs/orangepi_pc2_defconfig

 CONFIG_ARM=y
 CONFIG_ARCH_SUNXI=y
-CONFIG_SPL_SPI_FLASH_SUPPORT=y
 CONFIG_MACH_SUN50I_H5=y
 CONFIG_DRAM_CLK=672
 CONFIG_DRAM_ZQ=3881977

configs/orangepi_zero_defconfig

 CONFIG_ARM=y
 CONFIG_ARCH_SUNXI=y
-CONFIG_SPL_SPI_FLASH_SUPPORT=y
 CONFIG_MACH_SUN8I_H3=y
 CONFIG_DRAM_CLK=624
 CONFIG_DRAM_ZQ=3881979

drivers/mtd/spi/Kconfig

@@ -140,6 +140,7 @@ if SPL
 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
+	select SPL_SPI_FLASH_SUPPORT
 	---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