drm/i915: Remove superfluous GEN8_LR_CONTEXT_ALIGN

As GEN8_LR_CONTEXT_ALIGN is I915_GTT_MIN_ALIGNMENT is it functionally
equivalent to 0, and we will not be able to reduce the min-alignment for
the GTT, so passing 0 is and will remain equivalent.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180727092947.1953-1-chris@chris-wilson.co.uk