hwc: vds: Add support to dump layers, FB and WB output buffer

1. Add hook to dump the layers going to VDS based virtual display.

2. Furthermore, add utility function to dump the frame buffer and
   WB output buffer. This will be enabled via a system property

   debug.hwc.enable_vds_dump

   Once dumping is enabled, the dumps can be extracted from

   /data/vds.fb.FORMAT.XRESxYRES.raw
   /data/vds.wb.FORMAT.XRESxYRES.raw

   e.g. vds.fb.MDP_RGBA_8888.1152x1920.raw

Change-Id: I2435c5507961a52929411206892c005492d5c193
diff --git a/libhwcomposer/hwc_utils.h b/libhwcomposer/hwc_utils.h
index c7b7ded..5086d72 100644
--- a/libhwcomposer/hwc_utils.h
+++ b/libhwcomposer/hwc_utils.h
@@ -257,6 +257,7 @@
 
 bool canUseMDPforVirtualDisplay(hwc_context_t* ctx,
                                 const hwc_display_contents_1_t *list);
+void dumpBuffer(private_handle_t *ohnd, char *bufferName);
 
 //Helper function to dump logs
 void dumpsys_log(android::String8& buf, const char* fmt, ...);