drm/i915: Use drm_i915_private as the native pointer for intel_uncore.c

Pass drm_i915_private to the uncore init/fini routines and their
subservients as it is their native type.

   text    data     bss     dec     hex filename
6309978 3578778  696320 10585076         a183f4 vmlinux
6309530 3578778  696320 10584628         a18234 vmlinux

a modest 400 bytes of saving, but 60 lines of code deleted!

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1462885804-26750-1-git-send-email-chris@chris-wilson.co.uk