Refactor InputHost and InputDriver

The host implementation of the HAL interface is largely done by the
InputDriver, so have it implement the opaque input_host_t type rather
than the InputHost itself. This allows the HAL interface to cast the
input_host_t pointer to an InputDriver pointer in order to implement
the host functionality.

Change-Id: I72de1e90eb6ee5e346c15707b8a6b793005bbccb
diff --git a/services/inputflinger/host/InputHost.cpp b/services/inputflinger/host/InputHost.cpp
index 51d3e6b..094200a 100644
--- a/services/inputflinger/host/InputHost.cpp
+++ b/services/inputflinger/host/InputHost.cpp
@@ -28,7 +28,7 @@
 
 void InputHost::registerInputDriver(InputDriverInterface* driver) {
     LOG_ALWAYS_FATAL_IF(driver == nullptr, "Cannot register a nullptr as an InputDriver!");
-    driver->init(this);
+    driver->init();
     mDrivers.push_back(driver);
 }