crypto: caam - move sec4_sg_entry to sg_sw_sec4.h

sec4_sg_entry structure is used only by helper functions in sg_sw_sec4.h.
Since SEC HW S/G entries are to be manipulated only indirectly, via these
functions, move sec4_sg_entry to the corresponding header.

Signed-off-by: Horia Geantă <horia.geanta@nxp.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>