arm: mvebu: Move CONFIG_SYS_TEXT_BASE to an address < 16 MiB

This patch moves CONFIG_SYS_TEXT_BASE to 0x00800000 for all Armada
XP / 38x boards in mainline U-Boot. This is done in preparation for
the ECC SDRAM scrubbing that needs to be done in the main U-Boot.
The SPL (previously bin_hdr) has already scrubbed the area:
  0x0000.0000 - 0x0100.0000

In this area this main U-Boot needs to get loaded. The main U-Boot
then can scrub the remaining SDRAM area while running from this
location.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Luka Perkov <luka.perkov@sartura.hr>