pipe-loader: move dup(fd) within pipe_loader_drm_probe_fd

pipe-loader: move dup(fd) within pipe_loader_drm_probe_fd

Currently pipe_loader_drm_probe_fd takes ownership of the fd given.
To match that, pipe_loader_release closes it.

Yet we have many instances which do not want the change of ownership,
and thus duplicate the fd before passing it to the pipe-loader.

Move the dup() within pipe-loader, explicitly document that and document
all the cases through the codebase.

A trivial git grep -2 pipe_loader_release makes things as obvious as it
gets ;-)

Cc: Leo Liu <leo.liu@amd.com>
Cc: Thomas Hellstrom <thellstrom@vmware.com>
Cc: Axel Davy <davyaxel0@gmail.com>
Cc: Patrick Rudolph <siro@das-labor.org>
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Axel Davy <davyaxel0@gmail.com> (for nine)