scsi: Eliminate scsi_register() and scsi_unregister() usage & docs

scsi: Eliminate scsi_register() and scsi_unregister() usage & docs

scsi_mid_low_api.rst refers to scsi_register() and scsi_unregister() but
these functions don't exist. They have been replaced by more meaningful
names.

Update one driver (megaraid_mbox.c) that uses "scsi_unregister" in a
warning message. Update scsi_mid_low_api.rst to eliminate references to
scsi_register() and scsi_unregister().

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/20241205041839.164404-1-rdunlap@infradead.org
Cc: James E.J. Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: Bart Van Assche <bvanassche@acm.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Cc: Kashyap Desai <kashyap.desai@broadcom.com>
Cc: Sumit Saxena <sumit.saxena@broadcom.com>
Cc: Shivasharan S <shivasharan.srikanteshwara@broadcom.com>
Cc: Chandrakanth patil <chandrakanth.patil@broadcom.com>
Cc: megaraidlinux.pdl@broadcom.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>