test(xlat) : fix testcase xlat v2: Stress test

Testcase fails when test tries to unmap memory region
with size=0, mapping region with size=0 was success,
added workaround to skip mapping if size=0,
Will need to be fixed in xlat library later.

Change-Id: Icf326cf4889b833e1bd9e064eeeb1f309ae147c6
Signed-off-by: Shruti Gupta <shruti.gupta@arm.com>
1 file changed