drm/i915: STOP_MACHINE is no more, stop selecting it

The STOP_MACHINE kconfig symbol was removed upstream after making
stop_machine() always work, commit 86fffe4a ("kernel: remove
stop_machine() Kconfig dependency"), and was removed from i915's Kconfig
in commit 21fabbeb ("drm/i915: Remove select to deleted
STOP_MACHINE from Kconfig").

However, I accidentally reintroduced the select when rebasing an older
commit that also was dependent upon a working stop_machine.

Fixes: 9f267eb8 ("drm/i915: Stop the machine whilst capturing...")
Reported-by: Valentin Rothberg <valentinrothberg@gmail.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20161019180635.27459-1-chris@chris-wilson.co.ukReviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

drivers/gpu/drm/i915/Kconfig

@@ -4,7 +4,6 @@ config DRM_I915
 	depends on X86 && PCI
 	select INTEL_GTT
 	select INTERVAL_TREE
-	select STOP_MACHINE
 	# we need shmfs for the swappable backing store, and in particular
 	# the shmem_readpage() which depends upon tmpfs
 	select SHMEM