fbdevhw: Support symbolic links in fbdev_open

Commit Message

Resolve symbolic links before the PCI device check in fbdev_open.
Otherwise, opening device files that are symbolic links will fail.

Fixes: https://gitlab.freedesktop.org/xorg/xserver/-/issues/1419

Signed-off-by: Moritz Bruder <muesli4@gmail.com>

Testing Done

I successfully built and tested it on my Raspberry Pi where I have a path that is a symbolic link for the fbdev key in my configuration.

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