Fix libsp/opteesp build failure

When building the mentioned deployment an error is reported
complaining SP_HEAP_SIZE being undefined. This change fixes the
issue by adding a dummy definition. This setting only affects files
not used in this deployment.

Signed-off-by: Gyorgy Szing <Gyorgy.Szing@arm.com>
Change-Id: I542f9adf0fb0bb924959242a3a7873f56e890028
1 file changed