libaudiohal: Implement simple HIDL client

This client requires both HIDL client and server to be of the same
ABI version (e.g. 32-bit).

EffectHalHidl::process and EffectHalHidl::processReverse are stubs.

Some extra warnings are logged due to unimplemented functions
in the legacy HAL.

Bug: 30222631
Change-Id: Id074131dec6d6c4f1031695abcf3ea066e92a5af
Test: Play Music (play / EQ), YouTube, Loopback RTLT, Ok Google on N5X
diff --git a/media/libmedia/AudioParameter.cpp b/media/libmedia/AudioParameter.cpp
index d244a0a..65fc70b 100644
--- a/media/libmedia/AudioParameter.cpp
+++ b/media/libmedia/AudioParameter.cpp
@@ -189,6 +189,16 @@
     return result;
 }
 
+status_t AudioParameter::getAt(size_t index, String8& key) const
+{
+    if (mParameters.size() > index) {
+        key = mParameters.keyAt(index);
+        return NO_ERROR;
+    } else {
+        return BAD_VALUE;
+    }
+}
+
 status_t AudioParameter::getAt(size_t index, String8& key, String8& value) const
 {
     if (mParameters.size() > index) {