Add signbit support for f16 type

Resolves COMPMID-5037

Change-Id: I648e8810dfd86e2ebcc16554f3f4cc58a5fd8c32
Signed-off-by: SiCongLi <sicong.li@arm.com>
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/6899
Reviewed-by: Giorgio Arena <giorgio.arena@arm.com>
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
Tested-by: Arm Jenkins <bsgcomp@arm.com>
diff --git a/LICENSE b/LICENSE
index 1bb9056..953432d 100644
--- a/LICENSE
+++ b/LICENSE
@@ -1,6 +1,6 @@
 MIT License
 
-Copyright (c) 2017-2021 Arm Limited
+Copyright (c) 2017-2022 Arm Limited
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal