refactor: add new test-suite 'tests-timer-stress'

Moved 'Stress test timer framework' as part of 'tests-extensive' suite
by creating a separate test suite for timers, i.e. tests-timer-stress.

Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
Change-Id: Ibdad88e81fba55333c0ad17cc9c10d24d97e6c7e
diff --git a/tftf/tests/tests-extensive.mk b/tftf/tests/tests-extensive.mk
index d1c6c5e..5e0f006 100644
--- a/tftf/tests/tests-extensive.mk
+++ b/tftf/tests/tests-extensive.mk
@@ -6,6 +6,8 @@
 
 # Run all standard tests, plus the extensive ones.
 include tftf/tests/tests-standard.mk
-TESTS_MAKEFILE += tftf/tests/tests-psci-extensive.mk
+
+TESTS_MAKEFILE += tftf/tests/tests-psci-extensive.mk	\
+		  tftf/tests/tests-timer-stress.mk
 
 include ${TESTS_MAKEFILE}