sunxi: Kconfig: introduce CONFIG_SUNXI_HIGH_SRAM

sunxi: Kconfig: introduce CONFIG_SUNXI_HIGH_SRAM

Traditionally Allwinner SoCs have their boot ROM mapped just below 4GB,
while the first SRAM region is mapped at address 0.
With the extended physical memory support of the A80 this was changed,
so the BROM is now at address 0 and the SRAM region starts right behind
this at 64KB. This configuration seems to be called "high SRAM".
Instead of enumerating the SoCs which have copied this configuration,
let's call a spade a spade and introduce a Kconfig option for this setup.
SoCs implementing this (A80, A64 and H5, so far), can then select this
configuration.
Simplify the config header definition on the way.

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