drm/i915: Don't use GPU relocations prior to cmdparser stalls

drm/i915: Don't use GPU relocations prior to cmdparser stalls

If we are using the cmdparser, we will have to copy the batch and so
stall for the relocations. Rather than prolong that stall by adding more
relocation requests, just use CPU relocations and do the stall upfront.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170826135620.25949-1-chris@chris-wilson.co.uk
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>