Fix HDMI unblank behavior

Two issues:

(1) We were announcing the hotplug event before we were ready to
handle blank/unblank events, so we were losing the initial unblank
that power manager sends us when HDMI is first plugged in.  This
left the display blank until you toggled the device power off/on.

(2) We were retaining fbTargetHandle for HDMI after the display was
disconnected.  The value didn't get updated when HDMI was reconnected
because the display was blank, so we didn't go through that code
path.  So, when HDMI was re-connected, we passed stale data into
the HWC.

Bug 7323938

Change-Id: I2335d24fd7b0f00bb23fc63aa7bcf44cb8857c73

services/surfaceflinger/DisplayHardware/HWComposer.cpp

@@ -696,6 +696,7 @@ void HWComposer::disconnectDisplay(int disp) {
         free(dd.list);
         dd.list = NULL;
         dd.framebufferTarget = NULL;    // points into dd.list
+        dd.fbTargetHandle = NULL;
     }
 }
 

services/surfaceflinger/SurfaceFlinger.cpp

@@ -772,8 +772,7 @@ void SurfaceFlinger::onHotplugReceived(int type, bool connected) {
         }
         setTransactionFlags(eDisplayTransactionNeeded);
 
-        // we should only receive DisplayDevice::DisplayType from the vsync callback
-        mEventThread->onHotplugReceived(type, connected);
+        // Defer EventThread notification until SF has updated mDisplays.
     }
 }
 
@@ -1130,6 +1129,7 @@ void SurfaceFlinger::handleTransactionLocked(uint32_t transactionFlags)
                         DisplayDevice::makeCurrent(mEGLDisplay, hw, mEGLContext);
                         mDisplays.removeItem(draw.keyAt(i));
                         getHwComposer().disconnectDisplay(draw[i].type);
+                        mEventThread->onHotplugReceived(draw[i].type, false);
                     } else {
                         ALOGW("trying to remove the main display");
                     }
@@ -1212,6 +1212,7 @@ void SurfaceFlinger::handleTransactionLocked(uint32_t transactionFlags)
                                 state.viewport, state.frame);
                         hw->setDisplayName(state.displayName);
                         mDisplays.add(display, hw);
+                        mEventThread->onHotplugReceived(state.type, true);
                     }
                 }
             }