[SCSI] mpt2sas: Set max_sector count from module parameter

This feature is to override the default
max_sectors setting at load time, taking max_sectors as an
command line option when loading the driver.  The setting is
currently hard-coded in the driver to 8192 sectors (4MB transfers).
If max_sectors is specified at load time, minimum specified
setting will be 64, and the maximum is 8192.  The driver will
modify the setting to be on even boundary. If max_sectors is not
specified, the driver will default to 8192.

Signed-off-by: Kashyap Desai <kashyap.desai@lsi.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>