SF: add composer optional features

Test: SF unit tests

Change-Id: I7f177aae58d13e45dfdd54579722cec55dc21a3a
diff --git a/services/surfaceflinger/DisplayHardware/HidlComposerHal.cpp b/services/surfaceflinger/DisplayHardware/HidlComposerHal.cpp
index 18f24c1..5f8e434 100644
--- a/services/surfaceflinger/DisplayHardware/HidlComposerHal.cpp
+++ b/services/surfaceflinger/DisplayHardware/HidlComposerHal.cpp
@@ -153,6 +153,13 @@
     }
 }
 
+bool HidlComposer::isSupported(OptionalFeature feature) const {
+    switch (feature) {
+        case OptionalFeature::RefreshRateSwitching:
+            return mClient_2_4 != nullptr;
+    }
+}
+
 std::vector<IComposer::Capability> HidlComposer::getCapabilities() {
     std::vector<IComposer::Capability> capabilities;
     mComposer->getCapabilities(