drm/i915: dump the device info

Handy for lazy people like me, or when people forget to add the output
of lspci -nn.

v2: Chris Wilson noticed that we have this duplicated already in the
i915_capabilites debugfs file. But there \n as separator looks better,
which would be a bit verbose in dmesg. Abuse the preprocessor to
extract this all.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>