IVGCVSW-4158 FP16 Mobilenet V1 and V2 30% regression on ArmNN on Mate20

* Enable FP16 mixed precision for Android Q

Signed-off-by: Sadik Armagan <sadik.armagan@arm.com>
Change-Id: I5ddb94b13385e1fec39e4407dffc8e4bc6b8d64a
diff --git a/Android.mk b/Android.mk
index f8dcb60..d755d20 100644
--- a/Android.mk
+++ b/Android.mk
@@ -235,6 +235,7 @@
 
 ifeq ($(Q_OR_LATER),1)
 LOCAL_CFLAGS += \
+        -DARMNN_MIXED_PRECISION_FP16_POOLING \
         -DBOOST_NO_AUTO_PTR
 endif # PLATFORM_VERSION == Q or later