scsi: mpt3sas: Rename and export interrupt mask/unmask functions

Rename Function _base_unmask_interrupts() to
mpt3sas_base_unmask_interrupts() and _base_mask_interrupts() to
mpt3sas_base_mask_interrupts(). Also add function declarion to
mpt3sas_base.h

Link: https://lore.kernel.org/r/1596096229-3341-5-git-send-email-suganath-prabu.subramani@broadcom.com
Signed-off-by: Suganath Prabu S <suganath-prabu.subramani@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>