Add fp16 support for dequantize

* Changed RefDequantizeWorkload to use Encoder/Decoder
* Added related unit tests for Cl, Neon and Ref

Signed-off-by: Jan Eilers <jan.eilers@arm.com>
Change-Id: Ic2fd4103090dd2127c6859b49305736f7b2dfb05
diff --git a/src/backends/reference/backend.mk b/src/backends/reference/backend.mk
index 7e97acd..5f9af59 100644
--- a/src/backends/reference/backend.mk
+++ b/src/backends/reference/backend.mk
@@ -31,6 +31,7 @@
         workloads/Debug.cpp \
         workloads/DepthToSpace.cpp \
         workloads/DetectionPostProcess.cpp \
+        workloads/Dequantize.cpp \
         workloads/ElementwiseFunction.cpp \
         workloads/FullyConnected.cpp \
         workloads/Gather.cpp \