refactor(lib/s2tt): move the S2TT component to its own library

Minor renames also done as part of the refactor.

Signed-off-by: Javier Almansa Sobrino <javier.almansasobrino@arm.com>
Change-Id: If414cbd2669063853aebaa5d7c0b05ec36dc3c46
diff --git a/lib/realm/tests/buffer.cpp b/lib/realm/tests/buffer.cpp
index 444c61c..74a4d7c 100644
--- a/lib/realm/tests/buffer.cpp
+++ b/lib/realm/tests/buffer.cpp
@@ -348,7 +348,7 @@
 	cb.buffer_unmap = test_buffer_unmap_aarch64_vmsa;
 	(void)test_helpers_register_cb(cb, CB_BUFFER_UNMAP);
 
-	test_granule = realm_test_util_granule_struct_base() - 1U;
+	test_granule = test_helpers_granule_struct_base() - 1U;
 	slot = (enum buffer_slot)test_helpers_get_rand_in_range(
 						(unsigned long)(SLOT_NS + 1U),
 						(unsigned long)NR_CPU_SLOTS);
@@ -382,7 +382,7 @@
 	cb.buffer_unmap = test_buffer_unmap_aarch64_vmsa;
 	(void)test_helpers_register_cb(cb, CB_BUFFER_UNMAP);
 
-	test_granule = realm_test_util_granule_struct_base() +
+	test_granule = test_helpers_granule_struct_base() +
 							HOST_NR_GRANULES;
 	slot = (enum buffer_slot)test_helpers_get_rand_in_range(
 						(unsigned long)(SLOT_NS + 1U),