Fix the memory leak in virtualdisplay.cpp.

Fix the memory leak in virtualdisplay.cpp.
The memory leak causing the dmabuf fd that hwc opened increase all the time.
Causing the UI hang or reboot.
1: The buffer handle is without any 3D or framebuffer resource, thus it can
be destoryed directly instead of in the compositor thread
2: This will decoule the SetOuputBuffer and Present call. Previous it assumed
that SetOutputBuffer and Present is 1:1, but actually there is no guarantee from
the framework that it will be 1: This will decouple the SetOuputBuffer and Present call.
Previous it assumed that SetOutputBuffer and Present is 1:1, but actually there is no
guarantee from the framework that it will be 1:1

Jira:  https://jira01.devtools.intel.com/browse/OAM-67797
Tests: play video and UI doesn't hang or reboot. The fd that hwc opened is stable.

Signed-off-by: HeYue <yue.he@intel.com>