[SCSI] libsas: add SAS management protocol handler

This patch adds support for SAS Management Protocol (SMP) passthrough
support via bsg. aic94xx can use this.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>