[SCSI] raid_attrs: fix dependency problems

RAID attributes uses scsi_is_sdev_device() to gate some SCSI specific
checking code.  This causes two problems.  Firstly if SCSI == n just
defining scsi_is_sdev_device() to return false might not be enough to
prevent gcc from emitting the code (and thus referring to undefined
symbols), so this needs surrounding with an ifdef.  Secondly, using
scsi_is_sdev_device() when SCSI is either y or m gives a subtle
problem in the m case: raid_attrs must also be m to use the symbol.
Do the usual Kconfig jiggery-pokery to fix this.

Reported-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>