Platform: Increase stack size for an519 and an521

This patch increases the stack size for an519 and
an521 as it was too small to run the regression
tests.

Change-Id: I00ec6f7d325d13995f9e3e6edb322df866b44a57
Signed-off-by: Marc Moreno <marc.morenoberengue@arm.com>
2 files changed