hwc: In PTOR, offset depends on stride calculated by gralloc

1. In PTOR feature, offset for the second overlap layer on render
buffer, depends on stride calculated by gralloc for RGBA (4 bpp).

2. If mCopyBit object exists for external, we need setReleaseFd()

Change-Id: I74e365def2a6e540b2f2ba2b294b6b1e00e0ea96