ARM64: dts: Change corex reserve region

The reserved region for corex is currently placed in
the middle of the peripheral images region. This results in
conflicts when trying to remove the peripehral images region.
Move the corex region down below the peripheral region to avoid
conflicts.

Change-Id: Ide049c4bd5774e80a8fd5b47c3ba2ce6448723a8
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>