separate i915 suspend/resume functions into their own file

[Patch against drm-next.  Consider this a trial balloon for our new Linux
development model.]

This is a big chunk of code.  Separating it out makes it easier to change
without churn on the main i915_drv.c file (and there will be churn as we
fix bugs and add things like kernel mode setting).  Also makes it easier
to share this file with BSD.

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/i915/Makefile

@@ -3,7 +3,8 @@
 # Direct Rendering Infrastructure (DRI) in XFree86 4.1.0 and higher.
 
 ccflags-y := -Iinclude/drm
-i915-y := i915_drv.o i915_dma.o i915_irq.o i915_mem.o i915_opregion.o
+i915-y := i915_drv.o i915_dma.o i915_irq.o i915_mem.o i915_opregion.o \
+          i915_suspend.o
 
 i915-$(CONFIG_COMPAT)   += i915_ioc32.o