armv8: K3: j721e: Updated ddr address regions in MMU table

The A72 U-Boot code loads and boots a number of remote processors
including the C71x DSP, both the C66_0 and C66_1 DSPs, and the various
Main R5FSS Cores. In order to view the code loaded by the U-Boot by
remote cores, U-Boot should configure the memory region with right
memory attributes. Right now U-Boot carves out a memory region which
is not sufficient for all the images to be loaded. So, increase this
carve out region by 256MB.

Signed-off-by: Kedar Chitnis <kedarc@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>