this add functions for:
  - remove buffers from src/dst queue by index
  - remove exact buffer from src/dst queue

also extends m2m API to iterate over a list of src/dst buffers
in safely and non-safely manner.
Signed-off-by: NStanimir Varbanov <stanimir.varbanov@linaro.org>
Signed-off-by: NHans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@s-opensource.com>