drm/i915: Assert vma->flags are updated correctly during binding

drm/i915: Assert vma->flags are updated correctly during binding

As we bind, and unbind on error, we want to be sure that the vma->flags
are updated to reflect the binding state so that on the next invocation
all is well.

v2: Take two.
v3: Take three; vma-misplaced is checking map-and-fenceable so keep it
last!

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Matthew Auld <matthew.william.auld@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171105124550.32715-1-chris@chris-wilson.co.uk
Reviewed-by: Matthew Auld <matthew.william.auld@gmail.com>