corstone300: Modify ISRAM0 to be non-secure partition

A new patch is introduced to modify ISRAM0 to be
non-secure application storage while the secure data
would be placed inside Data tightly coupled memory (DTCM).

The reason behind this change is that ML applications
need more RAM memory than 1MB (ISRAM1 size) which is
the only current RAM storage available. However, with this
change we should have 2MB of RAM (ISRAM0 + ISRAM1 sizes) for
the application (non-secure side).

Signed-off-by: Ahmed Ismail <Ahmed.Ismail@arm.com>