Platform: Reduce stack size of test partitions

This change is necessary to fit to the available RAM
memory on Musca-A board, if isolation level is TFM_LVL=3.

Change-Id: I47248dcc10d757fb6b4fc9d26f1bd9adc83e5abb
Signed-off-by: Tamas Ban <tamas.ban@arm.com>
12 files changed