drm/i915: keep declarations in i915_drv.h

drm/i915: keep declarations in i915_drv.h

Fix sparse warnings:

drivers/gpu/drm/i915/i915_drv.c:1179:5: warning: symbol
'i915_driver_load' was not declared. Should it be static?

drivers/gpu/drm/i915/i915_drv.c:1267:6: warning: symbol
'i915_driver_unload' was not declared. Should it be static?

drivers/gpu/drm/i915/i915_drv.c:2444:25: warning: symbol 'i915_pm_ops'
was not declared. Should it be static?

Fixes: 42f5551d2769 ("drm/i915: Split out the PCI driver interface to i915_pci.c")
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1473946137-1931-3-git-send-email-jani.nikula@intel.com
(cherry picked from commit efab0698f94dd71fac5d946ad664a280441daedb)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>