[SCSI] megaraid_sas: Add input parameter for max_sectors

Driver add the input parameters support for max_sectors for megaraid
sas gen2 chip.  Customer can set the max_sectors support to 1MB for
gen2 chip during the driver load.

Signed-off-by Bo Yang <bo.yang@lsi.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>