drm/i915: Capture PCI revision and subsytem details in error state

Revision id along with device id is useful in better identification of the HW
and its limitations so include this detail in error state.

v2: make it clear that it is PCI revision and We might as well dump PCI
subsystem details while we update this (Ville, Chris).

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Arun Siluvery <arun.siluvery@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1454001521-7701-1-git-send-email-arun.siluvery@linux.intel.com