sunxi: move CONFIG_SPL_TEXT_BASE from *_defconfig to Kconfig

sunxi: move CONFIG_SPL_TEXT_BASE from *_defconfig to Kconfig

The choice of the SPL_TEXT_BASE is not really a decision that should be
specified by each board's defconfig, as this setting is actually
dictated by the SoC's memory map and the BootROM behaviour.

To make this obvious and reduce the clutter in the defconfig files,
let's specify the SoC constraints in the Kconfig stanza.
This allows us to remove these lines from the defconfig files again.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>