drm_hwcomposer: Fix HwcDisplay::GetDisplayIdentificationData()

Return Error::Unsupported in headless mode and if no EDID blob returned
by the kernel.

With this change GraphicsComposerHidlTest#GetDisplayIdentificationData
VTS no longer fails.

Also fix outPort assignment to avoid setting negative values
(handle_ is 0 for primary display).

Signed-off-by: Roman Stratiienko <roman.o.stratiienko@globallogic.com>
2 jobs for fix-getidentification in 9 minutes and 25 seconds (queued for 7 seconds)