scsi: megaraid_sas: add retry logic in megasas_readl

Due to hardware errata in Aero controllers, reads to certain fusion
registers could intermittently return zero.  This behavior is
transient in nature and subsequent reads will return valid value.

For Aero controllers, any calls to readl to read from certain
registers will be retried for maximum three times, if read returns
zero.

Signed-off-by: Shivasharan S <shivasharan.srikanteshwara@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>