[SCSI] fnic: fnic Driver Tuneables Exposed through CLI

Introduced module params to provide dynamic way of configuring
queue depth.

Added support to get max io throttle count through UCSM to
configure maximum outstanding IOs supported by fnic and push
that value to scsi mid-layer.

  Supported IO throttle values:

  UCSM IO THROTTLE VALUE        FNIC MAX OUTSTANDING IOS
  ------------------------------------------------------
        16 (Default)                    2048
        <= 256                          256
        > 256                           <ucsm value>

Signed-off-by: Hiral Patel <hiralpat@cisco.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>