lib/scatterlist: introduce sg_pcopy_from_buffer() and sg_pcopy_to_buffer()

lib/scatterlist: introduce sg_pcopy_from_buffer() and sg_pcopy_to_buffer()

The only difference between sg_pcopy_{from,to}_buffer() and
sg_copy_{from,to}_buffer() is an additional argument that specifies the
number of bytes to skip the SG list before copying.

Signed-off-by: Akinobu Mita <[email protected]>
Cc: "David S. Miller" <[email protected]>
Cc: "James E.J. Bottomley" <[email protected]>
Cc: Douglas Gilbert <[email protected]>
Cc: Herbert Xu <[email protected]>
Cc: Horia Geanta <[email protected]>
Cc: Imre Deak <[email protected]>
Acked-by: Tejun Heo <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>