[SCSI] scsi: Add osd library to build system

OSD in kernel source code is assumed to be at:
drivers/scsi/osd/ with its own Makefile and Kconfig

Add includes to them from drivers/scsi Makefile and Kconfig
Add OSD to MAINTAINERS file

Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Reviewed-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>