drm/i915/gem: Clear read/write domains for GPU clear

Update the domains for the write via the GPU so that we do not
shortcircuit any set-domain clflush afterwards.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=110978
Fixes: b2dbf8d9

 ("drm/i915/blt: Remove recursive vma->lock")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190624141630.11015-1-chris@chris-wilson.co.uk