i915: Move i915_read/write out of line

With the tracing code in there they are far too big to inline.

.text savings compared to a non force inline kernel:

i915_restore_display                        4393   12036   +7643
i915_save_display                           4295   11459   +7164
i915_handle_error                           2979    6666   +3687
i915_driver_irq_handler                     2923    5086   +2163
i915_ringbuffer_info                         458    1661   +1203
i915_save_vga                                  -    1200   +1200
i915_driver_irq_uninstall                    453    1624   +1171
i915_driver_irq_postinstall                  913    2078   +1165
ironlake_enable_drps                         719    1872   +1153
i915_restore_vga                               -    1142   +1142
intel_display_capture_error_state            784    2030   +1246
intel_init_emon                              719    2016   +1297

and more ...

[AK: these are older numbers, with the new SNB forcewake checks
it will be even worse]

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Keith Packard <keithp@keithp.com>