[SCSI] aacraid: expanded expose physical device code (new)

Received from Mark Salyzyn,

Take the expose_physicals flag and allow the user to select default (physicals
available via /dev/sg), exposed (physicals available via /dev/sd for
experimental reasons) and hidden (physicals blocked from all access). This
expands the functionality of the previous expose_physicals insmod parameter
which was added to support some experimental configurations.

Signed-off-by Mark Haverkamp <markh@linux-foundation.org>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>