cleanup asm/scatterlist.h includes

Not architecture specific code should not #include <asm/scatterlist.h>.

This patch therefore either replaces them with
#include <linux/scatterlist.h> or simply removes them if they were
unused.

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>