arty/base: change SoCSDRAM memory map
arty/base: change SoCSDRAM memory map

This reverts the map to the state before the commit 9d170b0 in LiteX,
as the new one does not work with VexRiscv in linux variant.

mithro/HDMI2USB-litex-firmware,mithro/HDMI2USB-litex-firmware,mithro/HDMI2USB-litex-firmware,mithro/HDMI2USB-litex-firmware