[SCSI] megaraid_sas: support for poll_mode_io (reduced interrupt)

Added module parameter "poll_mode_io" to support for "polling"
(reduced interrupt operation).  In this mode, IO completion interrupts
are delayed. At the end of initiating IOs, the driver schedules for
cmd completion if there are pending cmds.  A timer-based interrupt has
also been added to prevent IO completion from being delayed
indefinitely in the case that no new IOs are initiated.  Some
formatting issues in resume, suspend comment block also corrected

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