sunxi: move CONFIG_SYS_TEXT_BASE out of defconfigs

Commit 278b90ce

 ("configs: Migrate CONFIG_SYS_TEXT_BASE") made
CONFIG_SYS_TEXT_BASE a proper Kconfig variable, with the consequence
of moving the common definition shared by almost every sunxi board
into 123 individual defconfig files. But the U-Boot start address
for Allwinner boards is a platform decision which has been around for
ages, so defining it in each *board* config file seems a bit over the
top.
Define the standard values (160MB into DRAM for most SoCs, with two
SoC exceptions) if ARCH_SUNXI is selected, and delete the lines from
the individual defconfigs.

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