Enable Slice EndToEndTests in all backends and Signed32 in CpuRef

 * Enable SliceEndToEnd tests on CpuRef, CpuAcc, GpuAcc
 * Enable Signed32 support for slice in CpuRefLayerSupport

Signed-off-by: Ryan OShea <ryan.oshea3@arm.com>
Change-Id: Ie9907c65dcb0eb2f2f346b22541ebfc692a109cb
diff --git a/src/backends/reference/RefLayerSupport.cpp b/src/backends/reference/RefLayerSupport.cpp
index 2e845a8..6323db1 100644
--- a/src/backends/reference/RefLayerSupport.cpp
+++ b/src/backends/reference/RefLayerSupport.cpp
@@ -2436,7 +2436,8 @@
         DataType::Float32,
         DataType::QAsymmS8,
         DataType::QAsymmU8,
-        DataType::QSymmS16
+        DataType::QSymmS16,
+        DataType::Signed32
     };
 
     supported &= CheckSupportRule(TypeAnyOf(input, supportedTypes), reasonIfUnsupported,