This allows us to move scattered buffers around.

v2: fix a couple of typos, handle scattered to scattered moves as well.
Signed-off-by: NChristian König <christian.koenig@amd.com>
Reviewed-by: NEdward O'Callaghan <funfunctor@folklore1984.net>
Tested-by: NMike Lothian <mike@fireburn.co.uk>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>